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Phosphoenolpyruvate Carboxylase(EC 4.1.1.31, PEPC) is wide spread among all plants, including C3, C4, and CAM plants, with different biological functions. It catalyzes the irreversible β-carboxylation of phosphoenolpyruvate in the presence of HCO－3 to yield oxaloacetate and Pi. In this study, PEPC has been successfully purified from rice roots to reach a final 278-fold purification and total 35% recovery. The native molecular mass was determined to be 420 kDa composed of four subunits by gel-filtration chromatography and SDS-PAGE. The activity of purified PEPC was induced by glucose-6-phosphate to 126% and has 96% inhibition by L-malate at the pH 7.3. Meanwhile, rice root form PEPC can be phosphorylated by both rice and maize PEPC kinases in vivo. The results implied that PEPC might be regulated by phosphorylation as found in other forms. The PEPC can be detected from different tissues of rice by anti-PEPC antibody induced by purified PEPC in rice roots from rabbit serum. There were four distinct isoforms in different tissues, including two house keeping isoforms, 115 and 108 kDa, and two photosynthesis related isoforms, 112 and 105 kDa, respectively. These two photosynthetic related isoforms appeared during greening development were found only in leaves and shoots in rice. On the other hand, nitrogen also disturbed both the activity and the level of PEPC in vegetative stage leaves of rice. The activity and levelof PEPC were increased 205% and 124%, respectively. These results indicated that PEPC correlated with nitrogen assimilation in C3 plants.
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