Abstract
In the Calvin cycle, activities of thiol-modulated enzymes such as NADP+-GAPDH, FBPase, SBPase, and PRK are activated by reduction of intramolecular disulfide bridges via the ferredoxin/thioredoxin system. We demonstrated previously that the thiol-modulated enzymes from cyanobacteria and eukaryotic algae were not sensitive to treatment with DTT in vitro and were not regulated by light illumination in vivo, unlike these enzymes of higher plants. We focused on CP12 as a regulatory factor of the Calvin cycle in cyanobacteria. In cyanobacterial cells, the reversible dissociation of PRK/CP12/GAPDH complex was mediated by the change of NADP(H):NAD(H) ratio under light/dark conditions (Plant J. 42, 504, 2005). Furthermore, the oligomerization of CP12 together with PRK and NADP+-GAPDH regulated the activities of these enzymes and changed the carbon flow from the Calvin cycle to oxidative pentose phosphate cycle in the dark conditions.
