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.