photorespiration

RuBisCo & ITS ROLE IN

PHOTORESPIRATION

By-Narayan Prahlad.VV Semester Mol.Bio

9/9/2014

Contents

Introduction RuBisCo Activation of RuBisCo Function Photorespiration Conclusion Reference Acknowledgement

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.

RuBisCo

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

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.

Activation of RuBisCo

RuBisCo RuBisCo Lys (NH3+) Lys

NH2 Lys NH

Coo-

CO2H+

RuBisCo Lys NH COO-Mg2+

ACTIVE COMPLEX

RuBisCoH+

Mg2+

Functions

• Dual role-Carboxylation of RUDP & Oxygenase Activity.

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.

Photorespiration

Site of Photorespiration: Normal respiration in cytosol and

Mitochondria.

Here it occurs in three organelles with coordination- Chloroplast, Peroxisomes & Mitochondria.

Photorespiration

Conditions for Photorespiration:LightTemperature—25-35⁰COxygen-High concentrationCO2-Low Concentration.

Photorespiration

MECHANISM: In Chloroplast—

2-Phosphoglycolic acid

2-Phosphoglycolic acid Glycolic Acid

RuBisCo

Phosphatase

RUDP + O2

+ H2O

H2O2 2H2O + O2

Glycolic acid Glyoxylic acid

Catalase

G.A.oxidase + H2O2+ O2

In Peroxisomes

Glyoxylic acid Glutamic AcidGlycine

α-Ketoglutaric acid

GlyoxalateAmino transferase+

+

• In Mitochondria

Glycine Serine

Dehydrogenase

Decarboxylase 2mols +H2O+NAD

CO2+NH3+NADH2

+

• In Peroxisomes

Hydroxy pyruvic acid

Glycine

Glyoxylic amino transferase

Glyoxylic acid Serine+

+

Hydroxy pyruvic acidGlyceric Acid

+ NADHydroxy pyruvate reductase

• In Chloroplast

PGA

Glyceric acid kinase

Glyceric Acid

+ ATP

This PGA-joins with PGA of Calvin’s cycle –synthesis of carbohydrates.

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 intermediatesProtects from photoinhibition.

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

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.