Regulatory phosphorylation of plant phosphoenolpyruvate carboxylase: Role of a conserved basic residue upstream of the phosphorylation site

In order to mimic regulatory phosphorylation of the Ser-15 of maize C-4-form phosphoenolpyruvate carboxylase (PEPC), we replaced Ser-15 and Lys-12 with Asp (S15D) and Asn (K12N), respectively, by site-directed mutagenesis, Although both mutant enzymes mere catalytically as active as the mild-type PEPC, they showed much less sensitivity to malate, an allosteric inhibitor, similarly to the phosphorylated mild-type PEPC, A maize protein kinase of 30 kDa which is known to be specific to PEPC (PEPC-PK), phosphorylated K12N as well as the wild-type PEPC but not S15D, The phosphorylation of K12N further diminished the sensitivity to malate, Thus, a positive charge of the conserved Lys-12 is not required for the recognition by PEPC-PK but contributes to the intrinsic sensitivity to malate inhibition. (C) 1997 Federation of European Biochemical Societies.