This presentation discusses the regulation of the Calvin cycle by Muhammad Usman Mughal. It begins with an introduction to the Calvin cycle and then examines four main systems that regulate the cycle: 1) the rubisco enzyme activation system, 2) the ferredoxin-thioredoxin system, 3) ionic movement that modulates enzymes, and 4) the formation of supramolecular enzyme complexes. It focuses on how light and carbon dioxide levels affect these regulatory systems and the activities of key Calvin cycle enzymes.

2. Presented by: Muhammad Usman Mughal
Roll Number: 25
Class: Msc Botany 3rd Semester
Session: 2013-2015

3. 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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5.  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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7.  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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8.  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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9.  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 rubisco
1) activate the enzyme 2) substrate for carboxylation
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10.  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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11.  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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12.  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-carbamate
complex)
 Enzymes require Mg2+ are more active at pH 8 than 7
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13.  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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15. Taiz, T. and Zeiger, E. 2006, Plant physiology, 4th
Edition, pp 205 to 208.
https://www.boundless.com/microbiology/textbook
s/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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