Resolving the Activation Site of PositiveRegulators in Plant PhosphoenolpyruvateCarboxylase

Dear Editor, Phosphoenolpyruvate carboxylase （PEPC; EC 4.1.1.31） islocated at an important branch point in the carbohydratemetabolism of plants. The enzyme is a homotetramer andcatalyzes the addition of bicarbonate to phosphoenolpyru-vate （PEP） to form oxaloacetate and phosphate. PEPC isregulated by metabolites and phosphorylation. AIIostericfeedback inhibition is mainly regulated by L-malate andL-aspartate which bind to a site separated from the activecenter （Kai et al., 1999; Paulus et al., 2013）. Structure analy-sis of PEPC from Escherichia coli （Kai et al., 1999; Matsumuraet al., 2002）, Zea rnays （Matsumura et al., 2002）, Flaveria trin-ervia, and F. pringlei （Paulus et al., 2013） revealed that thesubstrate PEP and the feedback inhibitors bind to separatesites within each monomer.