ISOLATION AND SEQUENCE OF AN ACTIVE-SITE PEPTIDE FROM MAIZE LEAF PHOSPHOENOLPYRUVATE CARBOXYLASE INACTIVATED BY PYRIDOXAL 5'-PHOSPHATE

An active-site peptide from maize (Zea mays L.) phosphoenolpyruvate carboxylase has been isolated, sequenced and identified in the primary structure following chemical modification/inactivation of the enzyme by pyridoxal 5' -phosphate and reduction with sodium borohydride. The amino acid sequence of the purified dodecapeptide is Val-Gly-Tyr-Ser-Asp-Ser-Gly-Ly*s-Asp-Ala-Gly-Arg, which corresponds exactly to residues 599-610 in the deduced primary sequence of the maize-leaf enzyme. Comparative analysis of the deduced amino acid sequences of the enzyme from Escherichia coli, Anacystis nidulans and C3, C4 and Crassulacean acid metabolism plants indicates that they all contain this specific lysyl group, as well as a high degree of sequence homology flanking this species-invariant residue. This observation suggests a critical role for Lys-606 during catalysis by maize phosphoenolpyruvate carboxylase. This represents the first identification of a specific, species-invariant active-site residue in the enzyme.