Dear Editor,Phosphoenolpyruvate carboxylase (PEPC) is the essential enzyme for initial carbon fixation in C4 photosynthesis.The C4-PEPC evolved from a non-photosynthetic C3 ancestor by subtle sequence changes resulting in distinctly different kinetic and regulatory characteristics (Svensson et al.,1997).Malate and aspartate,which are formed from the carboxylation product of PEPC,serve as feedback inhibitors of the PEPC (Wedding et al.,1990).