This document discusses the enzyme RuBisCo and its role in photorespiration in plants. RuBisCo is an important plant enzyme that catalyzes the fixation of carbon dioxide during photosynthesis. It contains large and small subunits that assemble into a complex. RuBisCo has a dual role in carboxylation and oxygenation. Photorespiration is a process where oxygen is consumed and carbon dioxide is released in the presence of light. It occurs across three organelles - chloroplasts, peroxisomes and mitochondria. The mechanism involves multiple steps where RuBisCo mistakenly incorporates oxygen instead of carbon dioxide, leading to the production and transport of intermediates between the organelles before they are returned

1. RuBisCo & ITS ROLE IN
PHOTORESPIRATION
By-
Narayan Prahlad.V
V Semester Mol.Bio
9/9/2014

2. Contents
 Introduction
 RuBisCo
 Activation of RuBisCo
 Function
 Photorespiration
 Conclusion
 Reference
 Acknowledgement

3. Introduction
• Ribulose-1,5 bis phosphate carboxylase/oxidase also
abbreviated as RuBisCo - an important plant enzyme-
catalyzing few important reactions.
• Most abundantly found protein in the world.
• Mainly helps in carbon fixation - atmospheric
CO2 energy rich molecules like glucose.
• Respiration - process of energy release by the
breakdown of substrate material.

4. RuBisCo
The enzyme has eight large subunits (blue) and eight small ones (gray), tightly
packed into a structure

5. RuBisCo
• Contains two types of protein subunits-Large
Chain & Small Chain.
A total of 8 large chains & 8 small chains
assemble to form a large complex of about.
• Large Chain gene (rbcL) - part of Chloroplast DNA
& Small Chain genes - associated with plant cell
DNA.
• Active site of this enzyme is on Large Chain.

6. Activation of RuBisCo
RuBisCo RuBisCo
Lys
(NH3+)
Lys
NH2
Lys
NH
Coo-
CO2
H+
RuBisCo
Lys
NH
COO-
Mg2+
ACTIVE COMPLEX
RuBisCo
H+
Mg2+

7. Functions
• Dual role-Carboxylation of RUDP & Oxygenase
Activity.

8. Photorespiration
• Respiration-Process of energy release by the
breakdown of substrate material.
• In plants respiration is seen in dark as well as
in light.
Phenomenon of consumption of oxygen and
release of carbon-di-oxide in the presence of
light—Photorespiration.

9. Photorespiration
Site of Photorespiration:
 Normal respiration in cytosol and
Mitochondria.
Here it occurs in three organelles with
coordination- Chloroplast, Peroxisomes &
Mitochondria.

10. Photorespiration
Conditions for Photorespiration:
Light
Temperature—25-35⁰C
Oxygen-High concentration
CO2-Low Concentration.

11. Photorespiration
MECHANISM:
In Chloroplast—
2-Phosphoglycolic acid
2-Phosphoglycolic acid Glycolic Acid
RuBisCo
Phosphatase
RUDP + O2
+ H2O

12. H2O2 2H2O + O2
Glycolic acid
Glyoxylic acid
Catalase
G.A.oxidase + H2O2+ O2
In Peroxisomes

13. Glyoxylic acid Glutamic Acid
Glycine
α-Ketoglutaric acid
Glyoxalate
Amino transferase+
+

14. • In Mitochondria
Glycine Serine
Dehydrogenase
Decarboxylase
2mols +H2O+NAD
CO2+NH3+NADH2
+

15. • In Peroxisomes
Hydroxy pyruvic acid
Glycine
Glyoxylic amino transferase
Glyoxylic acid Serine
+
+

16. Hydroxy pyruvic acid
Glyceric Acid
+ NAD
Hydroxy pyruvate reductase

17. • In Chloroplast
PGA
Glyceric acid kinase
Glyceric Acid
+ ATP
This PGA-joins with PGA of Calvin’s cycle –synthesis
of carbohydrates.

18. Conclusion
• From the above discussion we conclude that
RuBisCo is a very important enzyme in plants
for energy production.
• Some uses of photorespiration are:
Removes toxic metabolic intermediates
Protects from photoinhibition.

19. Reference
•Lehninger, Principles of Biochemistry 5th
edition; David.L.Nelson & Micheal.M.Cox,
W. H. Freeman and Company,41 Madison
Avenue, New York, NY 10010,Houndmills,
Basingstoke RG21 6XS, England.
•www.ehow.com
•www.ebi.ac.uk

20. Acknowledgement
Sincere thanks to my guide Ragi
Jadimurthy for guiding me in this seminar
and Dr. NS Devaki for providing me this
opportunity.
Thank you all for your patient listening.