4. LIMITED PROTEOLYSIS
Peptide bond cleavage by specific enzymes =
proteases.
Limited cleaving of peptides.
New protein product new functions.
Classified = posttranslational modification.
5. PROTEASES
Exopeptidases = cleave near the N- or C-
terminus of peptides and proteins.
endopeptidases (proteinases) = cleave internal
peptide bonds in peptides and proteins.
6. PROTEIN DEGRADATION
Several sites on peptide are cleaved. Complete
degradation to AA.
Classified = protein turnover
Occurs in several compartments. Ex:
Lysosomes - acidified compartment, individual
proteases degrade proteins
Cytosol - ubiquitindependent proteasome system
degrades - at neutral pH.
7. LYSOSOMAL PROTEIN BREAKDOWN
Acidic pH
Various hydrolyses (proteases, nucleases..)
Significance –
degradation of extra/intracellular fragments
Phagocytosed microorganisms
Nutrition
Protein uptake:
Endocytosis
Autophagy
Phagocytosis
Specific targeting
8. UBIQUITIN-DEPENDENT PROTEIN
BREAKDOWN
Neutral pH
ATP-dependent degradation
Significance –
Digestion of proteins programmed for quick
destruction
Digestion of misfolding
Denaturated
Abnormal proteins