Calvin cycle regulation

Bistability and switching are crucial concepts of cellular regulation [80, 98] and can often be detected using the graphical methods outlined above. See also [98,287] for several illustrative examples. For a number of pathways, transitions between different states were observed, either in silico, in vivo, or both. Examples include the glycolytic pathway [273, 294], the Calvin cycle [113, 125], and models of the human erythrocytes [295, 296],... 

Triose phosphates produced by the Calvin cycle in bright sunlight, as we have noted, may be stored temporarily in the chloroplast as starch, or converted to sucrose and exported to nonphotosynthetic parts of the plant, or both. The balance between the two processes is tightly regulated, and both must be coordinated with the rate of carbon fixation. Five-sixths of the triose... 

Fridlyand, L.E. Scheibe R. (1999) Homeostatic regulation upon changes of enzyme activities in the Calvin cycle as an example for general mechanisms of flux control what can we expect from transgenic plants Photosynth. Res. 61, 227-239. 

Regulation of the Calvin Cycle Iodoacetate reacts irreversibly with the free —SH groups of Cys residues in proteins. 

Thioredoxin in Regulation of Calvin Cycle Enzymes Motohashi and colleagues used thioredoxin as a hook to fish out from plant extracts the proteins that are activated by thioredoxin. To do this, they prepared a mutant thioredoxin in which one of the reactive Cys residues was replaced with a Ser. Explain why this modification was necessary for their experiments. [Motohashi, K., Kondoh, A., Stumpp, M.T., Hisabori, T. (2001) Comprehensive survey of proteins targeted by chloroplast thioredoxin. Proc. Natl. Acad. Sci. USA 98, 11,224-11,229.]... 

Thioredoxin Plays a Key Role in Regulating the Calvin Cycle... 

Figure 20.14. Light Regulation of the Calvin Cycle. The light reactions of photosynthesis transfer electrons out of the... 

N. Wedel, J. Soil, and B.K. Paap. 1997. CP12 provides anew mode of light regulation of Calvin cycle activity in higher... 

N. Wedel and J. Soil. 1998. Evolutionary conserved light regulation of Calvin cycle activity by NADPH-mediated reversible phosphoribulokinase/CP12/glyceraldehyde-3-phosphate dehydrogenase complex dissociation Eroc. Natl. Acad. Sci. USA 95 9699-9704. (PubMed) (Full Text in PMC)... 

Chloroplast ferredoxin is a small water soluble protein M W 000) containing an Fe-S center [245]. Its midpoint potential ( — 0.42 V [246]) is suitable for acting as an electron acceptor from the PSI Fe-S secondary acceptors (Centers A and B) and as a donor for a variety of functions on the thylakoid membrane surface and in the stroma. Due to its hydrophylicity and its abundance in the stromal space, ferredoxin is generally considered as a diffusable reductant not only for photosynthetic non-cyclic and cyclic electron flow, but also for such processes as nitrite and sulphite reduction, fatty acid desaturation, N2 assimilation and regulation of the Calvin cycle enzyme through the thioredoxin system [245]. Its possible role in cyclic electron flow around PSI has already been discussed. The mobility of ferredoxin along the membrane plane could be an essential feature of this electron transfer process the actual electron acceptor for this function and the pathway of electron to plastoquinone is, however, still undefined. 

The Calvin cycle reactions that fix CO2 do not function in the dark. What are the likely reasons for this How are these reactions regulated by light ... 

See also Calvin Cycle, Pentose Phosphate Pathway, Regulation of Photosynthesis... 

F6P is a phosphorylated form of fructose commonly found in cells. F6P is an intermediate in glycolysis, gluconeogenesis, the pentose phosphate pathway, and the Calvin cycle. F6P is a substrate in biosynthesis of the important allosteric factor regulating glycolysis, fructose-2,6-bisphosphate and is also an important precursor of amino sugars (last enzyme below). 

List the four light-dependent changes in the stroma that regulate the Calvin cycle. 

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