In Vitro Phosphorylation of Maize Leaf Phosphoenolpyruvate Carboxylase

Numerous polypeptides in a leaf have been shown to undergo covalent modification by phosphorylation, but only a few have been identified to date. The results described herein demonstrate an Atp-dependent seryl phosphorylation of maize leaf PEPCase in comparison to the previously described Adp-dependent threonyl phosphorylation of maize leaf Ppdk (PEPCase and Ppdk have similar native and subunit relative masses). Phosphorylation of PEPCase resulted in a partial inactivation of the enzyme, whereas effector modulation by L-malate and glucose-6-phosphate was relatively unaffected. Both of these C4 mesophyll-cell enzymes are considered to catalyze key reactions during C4 photosynthesis.