Presented by: Muhammad Usman Mughal

Roll Number: 25

Class: Msc Botany 3rd Semester

Session: 2013-2015

1. Introduction

2. What is calvin cycle?

3. What is regulation of calvin cycle?

4. Rubisco enzyme activation system

5. Ferredoxin-thioredoxin system

6. Ionic movement modulate the enzymes

7. Formation of supramolecular complexes

8. Conclusion

9. References

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Carbon fixation cycle/ Reductive pentose phosphate cycle/ Calvin Benson cycle/ C3 cycle

Series of biochemical redox reactions in stroma of chloroplast

Independent of light

CO2 convert into carbohydrates in the presence of ATP,NADPH

Opposite to Kreb cycle/ citric acid cycle

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The rate of calvin cycle does not remain constant

All intermediates present in adequate concentration in light e.g CO2, ATP, NADPH, ions, Enzymes

Turned off when not needed in dark

Mainly regulate by the amount of enzymes in stroma

Light modulates the expression of stromal enzymes via specific photoreceptor (phytochrome and blue light receptor)

Structure and activity of enzyme modified by two methods 1) covalent bonds 2) ionic composition

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Calvin cycle itself independent of light but the enzymes which regulate calvin cycle are dependent on light

Light dependent modulation mechanism change the activity of five key enzymes

1. Rubsico

2. Fructose-1,6-bisphosphatase

3. Sedoheptul0se-1,7-bisphosphatase

4. Phosphoribulokinase

5. NADPH-glyceraldehyde-3-phosphate dehydrogenase

Generally there are four regulation systems

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Ribulose bisphosphate carboxylase

Most abundant protein on the earth to date

Activity of Rubisco increases in the light

CO2 play dual role in the activity of rubisco1) activate the enzyme 2) substrate for carboxylation

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Light controls the activity of four remaining enzyme via ferredoxin-thioredoxin system

1. Fructose-1,6-bisphosphatase

2. Sedoheptul0se-1,7-bisphosphatase

3. Phosphoribulokinase

4. NADPH-glyceraldehyde-3-phosphate dehydrogenase

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Ferredoxin-thioredoxin system consist of

1. Ferredoxin

2. Ferredoxin-thioredoxin reductase

3. Thioredoxin (regulatory protein)

Thioredoxin protect against damage caused by reactive oxygen species (H2O2, O2-,OH-)

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Due to illumination of light H+ moves from stroma to thylakoid space (pH of stroma increases from 7 to 8)

In this response of hydrogen ions, Mg2+ moves from thylakoid space to stroma (formation of E-carbamatecomplex)

Enzymes require Mg2+ are more active at pH 8 than 7

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Enzyme Phosphoribulokinase (PRK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) bound to CP12 (protein) with the help of disulfide bonds to hold the complex (supramolecular complex)

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Taiz, T. and Zeiger, E. 2006, Plant physiology, 4th

Edition, pp 205 to 208.

https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/microbial-metabolism-5/biosynthesis-52/regulation-of-the-calvin-cycle-339-7097/

http://en.wikipedia.org/wiki/Light-independent_reactions#Light-dependent_regulation

http://5e.plantphys.net/article.php?ch=8&id=81

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