Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
ENZYME
Dr. Deepak K Gupta
www.facebook.com/notesdental
Syllabus
• Definition, classification, specificity and active
site.
• Cofactors.
• Effect of pH temperature and substrate
...
Introduction
• Enzymes are biological catalysts synthesized by
living cells that accelerate biochemical reactions.
• The o...
Enzyme
• Enzymes are characterized by three distinctive
features:
• Catalytic Power
– Ability to catalyses biochemical rea...
Enzyme Nomenclature
• Traditionally, enzymes often were named by
adding the suffix –ase to the substrate upon
which they a...
Classification of Enzyme
• Enzyme are classified on the basis of action it performs
– Oxidoreductases - oxidation–reductio...
Intracellular and extracellular
enzymes
o Intracellular
o enzymes are synthesized and retained in the cell for the use of
...
Chemical Properties
• Most of enzymes carry out their functions relying solely
on their protein structure
• Many others re...
Chemical Properties
• If the enzyme is made of single polypeptide –
monomeric enzyme. Ex: ribonuclease, trypsin
• If the e...
www.facebook.com/notesdental
Enzyme Kinetics
• The quantitative measurement of the rates of
enzyme-catalyzed reactions and the systematic
study of fact...
Enzyme Kinetics
• Any biochemical reaction constitute,
A + B C + D
Where A and B are substrate and C + D are product
• Stu...
Gibs Free Energy Change ΔG
• Also called either free energy or Gibbs energy
• It describes in quantitative form both the d...
Activation Energy
• Any reaction doesn’t proceeds directly to product
formation.
• There is always a transition state betw...
Enzyme Kinetics
www.facebook.com/notesdental
Factors effecting enzyme activity
• The contact between enzyme and substrate is the
most essential pre-requisite for enzym...
Concentration of Substrate
• The frequency with which molecules
collide is directly proportionate to their
concentrations
...
Michaelis-Menten Constant Km
• Also known as Haldane’s Constant
• Substrate concentration to produce half
maximum velocity...
Michaelis-Menten Constant Km
Michaelis-Menten Reaction
www.facebook.com/notesdental
Concentration of Enzyme
• Reaction velocity is directly proportional to
concentration of enzyme
• Serum enzyme for diagnos...
Temperature
• Velocity of an enzyme reaction increase with the
increase in temperature up to a maximum and then
declines
•...
pH
• Most intracellular enzymes exhibit optimal activity at
pH values between 6 - 8.
• Balance between enzyme denaturation...
Activators
• Certain metallica cations – Mn, Mg, Zn, Ca, Co, Cu,
Na, K.
• It acts in a various ways
– Combining with subst...
Other Factor
• Product concentration: Accumulation of
reaction products generally decreases the
enzyme velocity
• Light an...
Mechanism of Enzyme Action: Active
Sites
• The active site of an enzyme is the region that
binds substrates, co-factors an...
Active Sites
This model (above) is an enzyme called
Ribonuclease S, that breaks up RNA
molecules. It has three active site...
Active site
o Active site can be further divided into:
it chooses the substrate It performs the catalytic
and binds it to ...
Mechanism of enzyme action
• The catalytic efficiency of enzymes is explained by two
perspectives:
Thermodynamic
changes
P...
Thermodynamic changes
• All chemical reactions have energy barriers between reactants and
products.
• The difference in tr...
Processes at the active site
Covalent
catalysis
Acid base
catalysisCatalysis
by strain
Catalysis
by
proximity
www.facebook...
Covalent catalysis
o Enzymes form covalent linkages with substrate forming transient enzyme-
substrate complex with very l...
acid-base catalysis
• Mostly undertaken by oxido- reductases enzyme.
• Mostly at the active site, histdine is present whic...
Catalysis by proximity
• In this catalysis molecules must come in bond forming distance.
• When enzyme binds:
 A region o...
Catalysis by bond strain
• Mostly undertaken by lyases.
• The enzyme-substrate binding causes reorientation of the structu...
Lock and key model
• Proposed by EMIL FISCHER in 1894.
• Lock and key hypothesis assumes the active site of an enzymes are...
Lock and Key Model
The lock and key model of enzyme action, proposed earlier this century,
proposed that the substrate was...
Induced fit model
• More recent studies have revealed that the process is much more likely to
involve an induced fit model...
Induced Fit Model
More recent studies
have revealed that the
process is much more
likely to involve an
induced fit.
The en...
39
Induced Fit Model
www.facebook.com/notesdental
Changing the Active Site
• Changes to the shape of the active site will result
in a loss of function. Enzymes are sensitiv...
Inhibition
o The prevention of an enzyme process as a result of interaction of
inhibitors with the enzyme.
 INHIBITORS:
A...
Types of inhibition
Inhibition
Reversible
Competitive Uncompetitive Mixed Non-competitive
Irreversible
www.facebook.com/no...
REVERSIBLE INHIBITION
o It is an inhibition of enzyme activity in which the inhibiting molecular
entity can associate and ...
Competitive inhibition
• In this type of inhibition, the inhibitors compete with the substrate for the
active site. Format...
Examples of competitive
inhibition
Statin Drug As Example Of Competitive
Inhibition:
• Statin drugs such as lipitor compe...
Uncompetitive Inhibition
• In this type of inhibition, inhibitor does not compete with the substrate for
the active site o...
Examples of
uncompetitive
inhibition
• Drugs to treat cases of poisoning by methanol or ethylene glycol
act as uncompetiti...
Non competitive
inhibition
o It is a special case of inhibition.
o In this inhibitor has the same affinity for either enzy...
Irreversible inhibition
• This type of inhibition involves the covalent attachment of the inhibitor to
the enzyme.
• The c...
Examples of irreversible
inhibition
• Aspirin which targets and covalently modifies a key enzyme involved in
inflammation ...
ENZYME SPECIFICITY
• Enzymes are highly specific in nature, interacting with one or few
substrates and catalyzing only one...
Types of enzyme
specificity
• Enzymes show different degrees of specificity:
 Bond specificity.
 Group specificity.
 Ab...
BOND SPECIFICITY
• In this type, enzyme acts on substrates that are similar in structure and
contain the same type of bond...
GROUP SPECIFICITY
• In this type of specificity, the enzyme is specific not only to the type of
bond but also to the struc...
SUBSTRATE SPECIFICITY
• In this type of specificity ,the enzymes acts only on one substrate
Example :
 Uricase ,which act...
OPTICAL / STEREO-SPECIFICITY
• In this type of specificity , the enzyme is not specific to substrate
but also to its optic...
DUAL SPECIFICITY
• There are two types of dual specificity.
 The enzyme may act on one substrate by two different reactio...
 The enzyme may act on two substrates by one reaction type
Example:
• Xanthine oxidase enzyme acts on xanthine and hypoxa...
Enzyme Regulation
• Regulation of enzyme occurs in following ways
– Allosteric regulation
– Activation of Latent Enzyme
– ...
Allosteric regulation
• Additional sites other than active sites –
Allosteric enzymes
• Types of allosteric enzyme:
– K-cl...
Activation of Latent Enzyme
• Some enzymes remain inactive,
• It gets activated at the site of action by the
breakdown of ...
Compartmentation
• The enzyme remains confined to particular area
of cell/body which makes it exclusive
• For instance: fa...
Control of enzyme synthesis
• Most of the enzyme particularly the rate limiting
ones are present in very low concentration...
Enzyme Degradation
• Enzymes have their self-destructing
capabilities.
• But it is highly variable and in general
– The ke...
Isoenzyme
• When same reaction is catalyzed by two or more
different molecular forms of an enzyme, it is
called isoenzyme
...
Diagnostic Importance of Enzyme
• Estimation of enzyme activities in biological
fluid is of great clinical importance.
• T...
Plasma Specific
• Present in the plasma normally and have specific
fucntion
• Their value is higher in plasma than tissue
...
Non-plasma specific
• These enzymes are present in the low level in
plasma compared to the tissue
• Estimation of activiti...
Important Diagnostic Enzymes
• Amylase – Acute pancreatitis
• Serum glutamate pyruvate transferase (SGPT) – liver
disease ...
Amylase
• Activity increased in acute pancreatitis
• Normal level – 0.2-1.5 IU/l
• Peak value in 8-12 hrs – onset of disea...
Serum glutamate pyruvate
transferase (SGPT)
• Also known as Alanine transaminase (ALT)
• Normal level – 3-4.0 IU/l
• Acute...
Serum glutamate oxaloacetate
transaminase (SGOT)
• Also known as Aspartate transaminase
• Normal 4-4.5 IU/l
• Increase in ...
Alkaline phosphatase
• Elevated in bone and liver disease
• Normal : 25-90 IU/l
• Diagnosis for
– Rickets,
– Hyperparathyr...
Acid phophatase
• Normal : 0.5 -4 KA units/dl
• Increased in cancer of prostate gland and
Paget’s Disease
• Good tumor mar...
Lactate dehydrogenase (LDH)
• At least five different isozymes
• Assess the timing and extent of heart damage
due to myoca...
Creatinine phosphokinase (CPK)
• Normal : 10-50 IU/l
• Diagnosis of
– MI - Very early detection
– Muscular dystrophy
– Hyp...
Aldolase
• Normal ; 2+6 IU/l
• Diagnosis of
– Muscular dystrophy
– Liver disease
– Myocardial infarction
– Myasthenia grav...
References
• Biochemistry – U. Satyanarayan, U. Chakerpeni
• Color_Atlas_of_Biochemistry_2005
• Harpers_Biochemistry_26th_...
Upcoming SlideShare
Loading in …5
×

Enzyme

55,590 views

Published on

Dental, biochemistry,

Published in: Health & Medicine
  • www.HelpWriting.net helped me too. I always order there
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • Have u ever tried external professional writing services like ⇒ www.WritePaper.info ⇐ ? I did and I am more than satisfied.
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • A professional Paper writing services can alleviate your stress in writing a successful paper and take the pressure off you to hand it in on time. Check out, please ⇒ www.HelpWriting.net ⇐
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • I thought I was good at writing essays all through freshman and sophomore year of high school but then in my junior year I got this awful teacher (I doubt you’re reading this, but screw you Mr. Murphy) He made us write research papers or literature analysis essays that were like 15 pages long. It was ridiculous. Anyway, I found ⇒ www.HelpWriting.net ⇐ and since then I’ve been ordering term papers from this one writer. His stuff is amazing and he always finishes it super quickly. Good luck with your order!
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • The Gout Eraser is a short, to the point guide on how to reverse gout symptoms without ever leaving your home. The guide goes into extensive detail on exactly what you need to do to safely, effectively and permanently get rid of gout, and you are GUARANTEED to see dramatic improvements in days if not hours. ♣♣♣ https://url.cn/5MYrgAB
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here

Enzyme

  1. 1. ENZYME Dr. Deepak K Gupta www.facebook.com/notesdental
  2. 2. Syllabus • Definition, classification, specificity and active site. • Cofactors. • Effect of pH temperature and substrate concentration. • Introduction to enzyme inhibitors, proenzymes and isoenzymes. • Introduction to allosteric regulation, covalent modification and regulation by induction / repression www.facebook.com/notesdental
  3. 3. Introduction • Enzymes are biological catalysts synthesized by living cells that accelerate biochemical reactions. • The orderly course of metabolic processes is only possible because each cell is equipped with its own genetically determined set of enzymes • It is only this that allows coordinated sequences of reactions - metabolic pathways • Involved in many regulatory mechanisms. • Almost all enzymes are proteins except catalytically active ribonucleic acids, the ribozymes www.facebook.com/notesdental
  4. 4. Enzyme • Enzymes are characterized by three distinctive features: • Catalytic Power – Ability to catalyses biochemical reaction – Accelerating reaction rates as much as 1016 over uncatalyzed levels - far greater than any synthetic catalysts • Specificity – A given enzyme is very selective – Both in the substances with which it interacts and in the reaction that it catalyzes • Regulation – Metabolic inhibitors and activators www.facebook.com/notesdental
  5. 5. Enzyme Nomenclature • Traditionally, enzymes often were named by adding the suffix –ase to the substrate upon which they acted • Ex: phosphatase, urease, catalase, proteases • Confusion arose from these trivial naming. • So a new system of nomenclature of enzyme was developed based on nature of reaction it helps • Six classes of reactions are recognized – Within each class are subclasses, and under each subclass are subsubclasses within which individual enzymes are listed www.facebook.com/notesdental
  6. 6. Classification of Enzyme • Enzyme are classified on the basis of action it performs – Oxidoreductases - oxidation–reduction reactions • Phosphate dehydrogenase – Transferases - transfer of functional groups • Methyltransferases, Carboxyltransferases – Hydrolases - hydrolysis reactions • Carboxylic ester hydrolases – Isomerases - isomerization reactions • Epimerases – Lyases - addition to double bonds • Carboxy lyases, Aldehyde lyases – Ligases - formation of bonds with ATP cleavage • Amino acid–RNA ligases www.facebook.com/notesdental
  7. 7. Intracellular and extracellular enzymes o Intracellular o enzymes are synthesized and retained in the cell for the use of cell itself. o They are found in the cytoplasm, nucleus, mitochondria and chloroplast. Example: Oxydoreductase catalyses biological oxidation, Enzymes involved in reduction in the mitochondria. o Extracellular o enzymes are synthesized in the cell but secreted from the cell to work externally. Example : Digestive enzyme produced by the pancreas, are not used by the cells in the pancreas but are transported to the duodenum. www.facebook.com/notesdental
  8. 8. Chemical Properties • Most of enzymes carry out their functions relying solely on their protein structure • Many others require non-protein components – cofactors – Usually metal ion or non-protein organic part (Coenzyme) • Less complex than proteins, tend to be stable to heat • Many coenzymes are vitamins or contain vitamins as part of their structure • Functional unit of enzyme is known as holoenzyme – Holenzyme = Apoenzyme + Coenzyme • Apoenzyme : protein without any catalytic activity www.facebook.com/notesdental
  9. 9. Chemical Properties • If the enzyme is made of single polypeptide – monomeric enzyme. Ex: ribonuclease, trypsin • If the enzyme is made up of more than one polypeptide – oligomeric enzyme. Ex: lactate dehydrogenase, aspartate transcarbamoylase • Multienzyme complex: have multiple enzyme unit to carry out different reaction in sequence www.facebook.com/notesdental
  10. 10. www.facebook.com/notesdental
  11. 11. Enzyme Kinetics • The quantitative measurement of the rates of enzyme-catalyzed reactions and the systematic study of factors that affect these rates • Helps in analysis, diagnosis, and treatment of the enzymic imbalances that underlie numerous human diseases. • Levels of particular enzymes serve as clinical indicators for pathologies – myocardial infarctions, – prostate cancer – damage to the liver www.facebook.com/notesdental
  12. 12. Enzyme Kinetics • Any biochemical reaction constitute, A + B C + D Where A and B are substrate and C + D are product • Study of enzyme kinetic has 2 component, i.e. • Gibs Free Energy : Direction and equilibrium state of substrate and product • Activation Energy: Mechanism of reaction and rate of reaction www.facebook.com/notesdental
  13. 13. Gibs Free Energy Change ΔG • Also called either free energy or Gibbs energy • It describes in quantitative form both the direction in which a chemical reaction will tend to proceed and the concentrations of substrate and products that will be present at equilibrium • Mathematically, ΔG = ΔGp – ΔGs – ΔGp : sum of the free energies of formation of the reaction products – ΔGs : sum of the free energies of formation of the substrates • The sign and the magnitude of the free energy change determine how far the reaction will proceed • If ΔG is negative then the reaction proceeds in forward direction spontaneously www.facebook.com/notesdental
  14. 14. Activation Energy • Any reaction doesn’t proceeds directly to product formation. • There is always a transition state between ground state and products • Activation energy: The difference between the energy levels of the ground state and the transition state. • The function of a catalyst is to increase the rate of a reaction, it does not affect reaction equilibria. • So enzyme just lowers the activation energy. www.facebook.com/notesdental
  15. 15. Enzyme Kinetics www.facebook.com/notesdental
  16. 16. Factors effecting enzyme activity • The contact between enzyme and substrate is the most essential pre-requisite for enzyme activity. • The important factors that influence the enzyme reaction are – Concentration of Substrate – Concentration of Enzyme – Temperature – pH – Product concentration – Activators – Time – Light and radiation www.facebook.com/notesdental
  17. 17. Concentration of Substrate • The frequency with which molecules collide is directly proportionate to their concentrations Rate ∝ [A]n[B]m , Rate = k[A]n[B]m – where, nA + mB → P; k = rate constant • The sum of the molar ratios of the reactants defines the kinetic order of the reaction • In the example above, reaction is said to be of (n+m) order overall but n order with respect to A and m order with respect to B www.facebook.com/notesdental
  18. 18. Michaelis-Menten Constant Km • Also known as Haldane’s Constant • Substrate concentration to produce half maximum velocity in an enzyme catalyst reaction • Km is constant and a chracterstic feature of a given enzyme – strength of Enzyme Substrate (ES) complex • Low Km value indicates a strong affinity between enzyme and substrate • Majority of Enzyme Km value – 10-5 to 10-2 www.facebook.com/notesdental
  19. 19. Michaelis-Menten Constant Km Michaelis-Menten Reaction www.facebook.com/notesdental
  20. 20. Concentration of Enzyme • Reaction velocity is directly proportional to concentration of enzyme • Serum enzyme for diagnosis of disease – Known volume of serum and substrate taken at optimum pH and temperature – Enzyme is assayed in laboratory www.facebook.com/notesdental
  21. 21. Temperature • Velocity of an enzyme reaction increase with the increase in temperature up to a maximum and then declines • Increase in temperature causes increases the kinetic energy of molecules • A bell-shaped curve is usually observed • Temperature coefficient Q10 : increase in enzyme velocity when the temperature is increased by 100C • Optimum temperature for most of enzyme – 40 – 45 0C • Beyond 500C there is denaturation of enzyme www.facebook.com/notesdental
  22. 22. pH • Most intracellular enzymes exhibit optimal activity at pH values between 6 - 8. • Balance between enzyme denaturation at high or low pH and effects on the charged state of the enzyme, the substrates, or both • Exception – pepsin (1-2), acid phosphatase (4-5), alkaline phophatase (10-11) www.facebook.com/notesdental
  23. 23. Activators • Certain metallica cations – Mn, Mg, Zn, Ca, Co, Cu, Na, K. • It acts in a various ways – Combining with substrate – Formation of E-S metal complex, direct participation in the reaction and bringing a conformational changes in enzyme • There are 2 categories of enzyme requiring metals for their activity • Metal activated enzyme:Not tightly held by the enzyme and can be exchanged easily. Ex: ATPAase (Mg and Ca) and Enolase • Metalloenzyme: Hold the metal tightly. Ex: alcohol dehydrogenase, carbonic anhydrase, alkaline phosphatase, carboxypeptidase www.facebook.com/notesdental
  24. 24. Other Factor • Product concentration: Accumulation of reaction products generally decreases the enzyme velocity • Light and radiation: exposure to UV, beta- gamma and X-rays inactivates certain enzyme – Formation of peroxides, ex: UV rays inhibit salivary amylase activity www.facebook.com/notesdental
  25. 25. Mechanism of Enzyme Action: Active Sites • The active site of an enzyme is the region that binds substrates, co-factors and prosthetic groups and contains residue that helps to hold the substrate. • Active sites generally occupy less than 5% of the total surface area of enzyme. • Active site has a specific shape due to tertiary structure of protein. • A change in the shape of protein affects the shape of active site and function of the enzyme. www.facebook.com/notesdental
  26. 26. Active Sites This model (above) is an enzyme called Ribonuclease S, that breaks up RNA molecules. It has three active sites (arrowed). Active site: The active site contains both binding and catalytic regions. The substrate is drawn to the enzyme’s surface and the substrate molecule(s) are positioned in a way to promote a reaction: either joining two molecules together or splitting up a larger one.Enzyme molecule: The complexity of the active site is what makes each enzyme so specific (i.e. precise in terms of the substrate it acts on). Substrate molecule: Substrate molecules are the chemicals that an enzyme acts on. They are drawn into the cleft of the enzyme. www.facebook.com/notesdental
  27. 27. Active site o Active site can be further divided into: it chooses the substrate It performs the catalytic and binds it to active site. action of enzyme. Active Site Binding Site Catalytic Site www.facebook.com/notesdental
  28. 28. Mechanism of enzyme action • The catalytic efficiency of enzymes is explained by two perspectives: Thermodynamic changes Processes at the active site www.facebook.com/notesdental
  29. 29. Thermodynamic changes • All chemical reactions have energy barriers between reactants and products. • The difference in transitional state and substrate is called activational barrier. www.facebook.com/notesdental
  30. 30. Processes at the active site Covalent catalysis Acid base catalysisCatalysis by strain Catalysis by proximity www.facebook.com/notesdental
  31. 31. Covalent catalysis o Enzymes form covalent linkages with substrate forming transient enzyme- substrate complex with very low activation energy. o Enzyme is released unaltered after completion of reaction. www.facebook.com/notesdental
  32. 32. acid-base catalysis • Mostly undertaken by oxido- reductases enzyme. • Mostly at the active site, histdine is present which act as both proton donor and proton acceptor. www.facebook.com/notesdental
  33. 33. Catalysis by proximity • In this catalysis molecules must come in bond forming distance. • When enzyme binds:  A region of high substrate concentration is produced at active site.  This will orient substrate molecules especially in a position ideal for them. www.facebook.com/notesdental
  34. 34. Catalysis by bond strain • Mostly undertaken by lyases. • The enzyme-substrate binding causes reorientation of the structure of site due to in a strain condition. • Thus transitional state is required and here bond is unstable and eventually broken. • In this way bond between substrate is broken and converted into products. www.facebook.com/notesdental
  35. 35. Lock and key model • Proposed by EMIL FISCHER in 1894. • Lock and key hypothesis assumes the active site of an enzymes are rigid in its shape. • There is no change in the active site before and after a chemical reaction. www.facebook.com/notesdental
  36. 36. Lock and Key Model The lock and key model of enzyme action, proposed earlier this century, proposed that the substrate was simply drawn into a closely matching cleft on the enzyme molecule. Substrate Enzyme Products Symbolic representation of the lock and key model of enzyme action. 1. A substrate is drawn into the active sites of the enzyme. 2. The substrate shape must be compatible with the enzymes active site in order to fit and be reacted upon. 3. The enzyme modifies the substrate. In this instance the substrate is broken down, releasing two products. www.facebook.com/notesdental
  37. 37. Induced fit model • More recent studies have revealed that the process is much more likely to involve an induced fit model(proposed by DANIAL KOSH LAND in 1958). • According to this exposure of an enzyme to substrate cause a change in enzyme, which causes the active site to change it’s shape to allow enzyme and substrate to bind. www.facebook.com/notesdental
  38. 38. Induced Fit Model More recent studies have revealed that the process is much more likely to involve an induced fit. The enzyme or the reactants (substrate) change their shape slightly. The reactants become bound to enzymes by weak chemical bonds. This binding can weaken bonds within the reactants themselves, allowing the reaction to proceed more readily. The enzyme changes shape, forcing the substrate molecules to combine. Two substrate molecules are drawn into the cleft of the enzyme. The resulting end product is released by the enzyme which returns to its normal shape, ready to undergo more reactions.www.facebook.com/notesdental
  39. 39. 39 Induced Fit Model www.facebook.com/notesdental
  40. 40. Changing the Active Site • Changes to the shape of the active site will result in a loss of function. Enzymes are sensitive to various factors such as temperature & pH. • When an enzyme has lost its characteristic 3D shape, it is said to be denatured. Some enzymes can regain their shape while in others, the changes are irreversible. www.facebook.com/notesdental
  41. 41. Inhibition o The prevention of an enzyme process as a result of interaction of inhibitors with the enzyme.  INHIBITORS: Any substance that can diminish the velocity of an enzyme catalyzed reaction is called an inhibitor. www.facebook.com/notesdental
  42. 42. Types of inhibition Inhibition Reversible Competitive Uncompetitive Mixed Non-competitive Irreversible www.facebook.com/notesdental
  43. 43. REVERSIBLE INHIBITION o It is an inhibition of enzyme activity in which the inhibiting molecular entity can associate and dissociate from the protein‘s binding site. TYPES OF REVERSIBLE INHIBITION o There are four types:  Competitive inhibition.  Uncompetitive inhibition.  Mixed inhibition.  Non-competitive inhibition. www.facebook.com/notesdental
  44. 44. Competitive inhibition • In this type of inhibition, the inhibitors compete with the substrate for the active site. Formation of E.S complex is reduced while a new E.I complex is formed. www.facebook.com/notesdental
  45. 45. Examples of competitive inhibition Statin Drug As Example Of Competitive Inhibition: • Statin drugs such as lipitor compete with HMG-CoA(substrate) and inhibit the active site of HMG CoA-REDUCTASE (that bring about the catalysis of cholesterol synthesis). www.facebook.com/notesdental
  46. 46. Uncompetitive Inhibition • In this type of inhibition, inhibitor does not compete with the substrate for the active site of enzyme instead it binds to another site known as allosteric site. www.facebook.com/notesdental
  47. 47. Examples of uncompetitive inhibition • Drugs to treat cases of poisoning by methanol or ethylene glycol act as uncompetitive inhibitors. • Tetramethylene sulfoxide and 3- butylthiolene 1-oxide are uncompetitive inhibitors of liver alcohaldehydrogenase. www.facebook.com/notesdental
  48. 48. Non competitive inhibition o It is a special case of inhibition. o In this inhibitor has the same affinity for either enzyme E or the E.S complex. MIXED INHIBITION o In this type of inhibition both E.I and E.S.I complexes are formed. o Both complexes are catalytically inactive. www.facebook.com/notesdental
  49. 49. Irreversible inhibition • This type of inhibition involves the covalent attachment of the inhibitor to the enzyme. • The catalytic activity of enzyme is completely lost. • It can only be restored only by synthesizing molecules. www.facebook.com/notesdental
  50. 50. Examples of irreversible inhibition • Aspirin which targets and covalently modifies a key enzyme involved in inflammation is an irreversible inhibitor. • SUICIDE INHIBITION :  It is an unusual type of irreversible inhibition where the enzyme converts the inhibitor into a reactive form in its active site. www.facebook.com/notesdental
  51. 51. ENZYME SPECIFICITY • Enzymes are highly specific in nature, interacting with one or few substrates and catalyzing only one type of chemical reaction. • Substrate specificity is due to complete fitting of active site and substrate . Example:  Oxydoreductase do not catalyze hydrolase reactions and hydrolase do not catalyze reaction involving oxidation and reduction. www.facebook.com/notesdental
  52. 52. Types of enzyme specificity • Enzymes show different degrees of specificity:  Bond specificity.  Group specificity.  Absolute specificity.  Optical or stereo-specificity.  Dual specificity. www.facebook.com/notesdental
  53. 53. BOND SPECIFICITY • In this type, enzyme acts on substrates that are similar in structure and contain the same type of bond. Example : • Amylase which acts on α-1-4 glycosidic ,bond in starch dextrin and glycogen, shows bond specificity. www.facebook.com/notesdental
  54. 54. GROUP SPECIFICITY • In this type of specificity, the enzyme is specific not only to the type of bond but also to the structure surrounding it. Example:  Pepsin is an endopeptidase enzyme, that hydrolyzes central peptide bonds in which the amino group belongs to aromatic amino acids e. g phenyl alanine, tyrosine and tryptophan. www.facebook.com/notesdental
  55. 55. SUBSTRATE SPECIFICITY • In this type of specificity ,the enzymes acts only on one substrate Example :  Uricase ,which acts only on uric acid, shows substrate specificity.  Maltase , which acts only on maltose, shows substrate specificity. www.facebook.com/notesdental
  56. 56. OPTICAL / STEREO-SPECIFICITY • In this type of specificity , the enzyme is not specific to substrate but also to its optical configuration Example:  D amino acid oxidase acts only on D amino acids.  L amino acid oxidase acts only on L amino acids. www.facebook.com/notesdental
  57. 57. DUAL SPECIFICITY • There are two types of dual specificity.  The enzyme may act on one substrate by two different reaction types. Example: • Isocitrate dehydrogenase enzyme acts on isocitrate (one substrate) by oxidation followed by decarboxylation(two different reaction types) . www.facebook.com/notesdental
  58. 58.  The enzyme may act on two substrates by one reaction type Example: • Xanthine oxidase enzyme acts on xanthine and hypoxanthine(two substrates) by oxidation (one reaction type) DUAL SPECIFICITY www.facebook.com/notesdental
  59. 59. Enzyme Regulation • Regulation of enzyme occurs in following ways – Allosteric regulation – Activation of Latent Enzyme – Compartmentation – Control of enzyme synthesis – Enzyme Degradation – Isoenzyme www.facebook.com/notesdental
  60. 60. Allosteric regulation • Additional sites other than active sites – Allosteric enzymes • Types of allosteric enzyme: – K-class: effectors changes the Km – V-class: effectors changes the Vmax • Most of allosteric enzymes are oligomeric in nature • Non-reversible binding of effector molecule at the allosteric sites – conformational change in the active site of enzyme www.facebook.com/notesdental
  61. 61. Activation of Latent Enzyme • Some enzymes remain inactive, • It gets activated at the site of action by the breakdown of one or more peptide bonds • Ex: chymotrypsin, pepsinogen and plasminogen • Certain enzymes keeps interconverting from active to inactive and vice-versa depending on the need of body • Ex: Glycogen phosphorylase, Phosphorylase b www.facebook.com/notesdental
  62. 62. Compartmentation • The enzyme remains confined to particular area of cell/body which makes it exclusive • For instance: fatty acid synthesis takes place in cytosol whereas fatty acid oxidation takes in mitochondria Organelle Enzyme/metabolic pathway Cytoplasm Aminotransferase, peptidases, glycolysis, HMP shunt Mitochondria Fatty acid oxidation, Kreb’s Cycle, Urea Cycle, ETC Nucleus Biosynthesis of DNA and RNA Endoplasmic Reticulum Protein Biosynthesis, Triacylglycrol and phospholipid synthesis Lysosomes Lysozyme, phosphatases, phospholipases, hydrolases, proteases Golgi Appartus Glucos-6 phosphatease, glucosyl and galactosyl transferase Peroxisomes Catalases, Urea oxidase, D-amino acid oxidase www.facebook.com/notesdental
  63. 63. Control of enzyme synthesis • Most of the enzyme particularly the rate limiting ones are present in very low concentration • Based on the amount of enzyme present in the body, enzymes are – Constitutive enzymes: its levels are not controlled and it remain almost constant – Adaptive enzymes: their level increases or decreases as per body needs • Synthesis of enzyme are regulated by gene. • Regulation by induction / repression www.facebook.com/notesdental
  64. 64. Enzyme Degradation • Enzymes have their self-destructing capabilities. • But it is highly variable and in general – The key and regulatory enzyme are most rapidly degraded – Not so important enzyme have longer half life • Ex: LDH4 – 5-6 days, LDH1 – 8-12 hrs, amylase – 3-5 hrs www.facebook.com/notesdental
  65. 65. Isoenzyme • When same reaction is catalyzed by two or more different molecular forms of an enzyme, it is called isoenzyme • It may occur in the same species, in the same tissue, or even in the same cell. • The different forms of the enzyme generally differ in kinetic or regulatory properties • Ex: hexokinase - 4, lactate dehydrogenase (LDH) – 5, creatinine phosphate (CPK) - 3 , creatinine kinase (CK) - 3, Alkaline phosphate (ALP) – 6, Alcohol dehydrogenase (ADH) - 2 www.facebook.com/notesdental
  66. 66. Diagnostic Importance of Enzyme • Estimation of enzyme activities in biological fluid is of great clinical importance. • The enzyme can be divided in 2 groups – Plasma Specific or plasma functional enzyme – Non-plasma specific or plasma non-functional enzyme www.facebook.com/notesdental
  67. 67. Plasma Specific • Present in the plasma normally and have specific fucntion • Their value is higher in plasma than tissue • They are mainly synthesized in liver and enter the circulation • Ex: Lipoprotein lipase, plasmin, thrombin, choline esterase, ceruloplasmin • Impairment of liver function or genetic disorder – leads to enzyme deficiency • Wilson disease – deficiency of ceruloplasmin www.facebook.com/notesdental
  68. 68. Non-plasma specific • These enzymes are present in the low level in plasma compared to the tissue • Estimation of activities of these enzymes serves for the diagnosis and prognosis of several disease - markers of disease • The raised enzyme level may indicate – Cellular damage – Increased rate of cell turnover – Proliferation of cells – Increased synthesis of enzymes www.facebook.com/notesdental
  69. 69. Important Diagnostic Enzymes • Amylase – Acute pancreatitis • Serum glutamate pyruvate transferase (SGPT) – liver disease (hepatitis) • Serum glutamate oxaloacetate transaminase (SGOT) – Heart attacks (myocardial infarction) • Alkaline phosphatase – Rickets, obstructive jaundice • Acid phophatase – cancer of prostate gland • Lactate dehydrogenase (LDH) – heart attacks, liver disease • Creatinine phosphokinase (CPK) – myocardial infarction • Aldolase – Muscular dystrophy www.facebook.com/notesdental
  70. 70. Amylase • Activity increased in acute pancreatitis • Normal level – 0.2-1.5 IU/l • Peak value in 8-12 hrs – onset of disease and returns to normal in 3-4 days • Urine analysis • Serum analysis – chronic pancreatitis, acute parotitis (mumps) and obstruction of pancreatic duct www.facebook.com/notesdental
  71. 71. Serum glutamate pyruvate transferase (SGPT) • Also known as Alanine transaminase (ALT) • Normal level – 3-4.0 IU/l • Acute hepatitis of viral or toxic origin • Jaundice and cirrohosis of liver www.facebook.com/notesdental
  72. 72. Serum glutamate oxaloacetate transaminase (SGOT) • Also known as Aspartate transaminase • Normal 4-4.5 IU/l • Increase in myocardial infarction and also in liver diseases • SGPT is more specific for liver disease and SGOT for MI – SGPT more cytosomal enzyme while SGOT is cytosol and mitochondria www.facebook.com/notesdental
  73. 73. Alkaline phosphatase • Elevated in bone and liver disease • Normal : 25-90 IU/l • Diagnosis for – Rickets, – Hyperparathyroidism, – Carcinoma of bone – Obstructive jaundice – Paget’s Disease www.facebook.com/notesdental
  74. 74. Acid phophatase • Normal : 0.5 -4 KA units/dl • Increased in cancer of prostate gland and Paget’s Disease • Good tumor marker www.facebook.com/notesdental
  75. 75. Lactate dehydrogenase (LDH) • At least five different isozymes • Assess the timing and extent of heart damage due to myocardial infarction MI (heart attack) – 12 hrs of MI: blood level of total LDH increases, and there is more LDH2 than LDH1 – 24 hrs of MI: more LDH1 than LDH2 Type Composition Location LDH1 HHHH Heart and erythrocyte LDH2 HHHM Heart and erythrocyte LDH3 HHMM Brain and kidney LDH4 HMMM Skeletal muscle and liver LDH5 MMMM Skeletal muscle and liver www.facebook.com/notesdental
  76. 76. Creatinine phosphokinase (CPK) • Normal : 10-50 IU/l • Diagnosis of – MI - Very early detection – Muscular dystrophy – Hypothyroidism – Alcoholism www.facebook.com/notesdental
  77. 77. Aldolase • Normal ; 2+6 IU/l • Diagnosis of – Muscular dystrophy – Liver disease – Myocardial infarction – Myasthenia gravis – Leukemia www.facebook.com/notesdental
  78. 78. References • Biochemistry – U. Satyanarayan, U. Chakerpeni • Color_Atlas_of_Biochemistry_2005 • Harpers_Biochemistry_26th_ed • Lehninger Principles of Biochemistry, Fourth Edition - David L. Nelson, Michael M. Cox. www.facebook.com/notesdental

×