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The Plant Phosphoeriolyruvate Carboxylase

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Phosphoenolpyruvate carboxylase (EC 4.1.1.31, PEPC) is a ubiquitous plant cytosolic enzyme and Widely distributed among all plants, including C3, C4, and CAM species. This enzyme which catalyzes the formation of oxaloacetate from phosphoenolpyruvate (PEP) and bicarbonate, plays a substantial role in the initial carbon fixation reaction in C4 and CAM plants (reviewed in Ref. 17) In these plants, mentioned reaction occurs in the mesophyll cells of the leaves. The generated oxaloacetate is converted into malate which is sent into the bundle-sheath cells. In these cells CO2 is released from the C4 compounds and raises the CO2concentration in the vicinity of ribulose-bisphosphate carboxylase/oxygenase (Rubisco), therefore the oxygenase activity of Rubisco and photorespiration would be suppressed. On the other hand, PEPC also plays multiple physiological roles in non-photosynthetic and C3 photosynthetic cells, which consist of the replenishment of tricarboxylic acid cycle to provide C skeletons for amino acid biosynthesis, adjustment of cellular pH and cation balance, NADPH production, re-trapping of respired CO2 and malate fermentation. With regard to its important functions, the properties and activity of PEPC have been widely studied. There are at least four different forms (alloenzymes) of PEP carboxylase in higher plants which are different from each other in some critical properties: a, C4-photosynthetic PEP carboxylase; b, CAM-PEP carboxylase; c, C3-photosynthetic PEP
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