Regulation of C4 photosynthesis: catalytic phosphorylation as a prerequisite for ADP-mediated inactivation of pyruvate,Pi dikinase.

Evidence is provided that the role of ATP in the ADP plus ATP-dependent inactivation of pyruvate,Pi dikinase is to catalytically phosphorylate the enzyme. Only this phosphorylated form of the enzyme is susceptible to inactivation by reacting with ADP. Phosphoenolpyruvate, which also phosphorylates pyruvate,Pi dikinase during catalysis, can replace the ATP-requirement for inactivation.