PEP carboxylase kinase is a novel protein kinase controlled at the level of expression

Phosphoenolpyruvate (PEP) carboxylase plays a number of key roles in the ce ntral metabolism of higher plants. The enzyme is regulated by reversible ph osphorylation in response to a range of signals in many different plant tis sues. The data discussed here illustrate several novel features of this sys tem. The phosphorylation state of PEP carboxylase is controlled largely by the activity of PEP carboxylase kinase. This enzyme comprises a protein kin ase catalytic domain with no regulatory regions. In many systems it is cont rolled at the level of expression. In C, plants, expression of PEP carboxyl ase kinase is light-regulated and involves changes in cytosolic pH, InsP(3) and Ca2+ levels. Expression of PEP carboxylase kinase in CAM plants is reg ulated by a circadian oscillator, perhaps via metabolite control. Some plan ts contain multiple PEP carboxylase kinase genes, probably with different e xpression patterns and roles. A newly discovered PEP carboxylase kinase inh ibitor protein might facilitate the net dephosphorylation of PEP carboxylas e under conditions in which flux through this enzyme is not required. (C) N ew Phytologist (2001) 151: 91-97.