Regulation of the Activation of Pyruvate, Pi Dikinase and NADP-malate Dehydrogenase in Maize

Abstract

In C4 plants two enzymes of the C4 cycle, pyruvate, Pi dikinase (PPDK) and NADP-malate dehydrogenase (NADP-MDH) are active in the light and inactive in the dark. Both enzymes are located in the mesophyll chloroplast and surprisingly, are activated by different mechanisms. NADP-MDH is activated via reduction of disulfide groups on the protein by thioredoxin or protein modulase mediated electron transfer through the noncyclic electron flow in the light (Buchanan 1980, Anderson et al. 1981). In the dark, the enzyme may be reoxidized by donating electrons to O2 via thioredoxin (Kagawa, Hatch 1977, see also Anderson et al. 1981).