PHOSPHOENOLPYRUVATE CARBOXYLASE - STRUCTURE, REGULATION AND EVOLUTION

Plant phosphoenolpyruvate carboxylase (EC 4.1.1.31; PEPC) is encoded b y a small multigene family in which the expression of each member is c ontrolled individually by exogenous (light, environmental) and/or endo genous (hormonal and developmental) stimuli. The involvement of putati ve trans-acting factors and consensus cis-elements of promoters in the specific transcriptional regulation of the PEPC genes is discussed. A t the post-translational level, the regulatory strategy of the plant e nzyme is mainly to offset the negative effect of the feedback inhibito r, L-malate, the end-product of the oxaloacetate reduction. All plant PEPC-forms are under positive and negative allosteric control by metab olite effecters and possess a consensus phosphorylation site containin g a target serine residue near their N-terminus (e.g. Ser8 in C-4 PEPC from sorghum). In C-4 and Crassulacean acid metabolism (CAM) plants, a complex signal-transduction chain activates a Ca2+-independent prote in-serine kinase responsible for regulatory phosphorylation of PEPC. A more thorough understanding of the functional and regulatory properti es of the bacterial and C-4 enzymes has emerged by exploiting recombin ant proteins and site-directed mutagenesis. In these newly opened area s, PEPC offers one of the best characterized paradigms of plant signal ing. Finally, some emerging ideas on the evolution and phylogenetic re lationships of the various PEPC isoforms are presented.