Phosphopyruvate carboxylase

The free glucose produced by this reaction is supplied to the blood from the tissues. As exemplified by gluconeogenesis, one may easily envision the economical organization of these metabolic routes, since, apart from four special gluconeogenesis enzymes-pyruvate carboxylase, phosphopyruvate carboxylase, fructose bisphosphatase, and glucose 6-phosphatase-individual glycolytic enzymes are also used in the gluconeogenesis. 

Phosphoenolpyruvate carboxykinase (GTP) [EC 4.1.1.32], also known as phosphoenolpyruvate carboxylase and phosphopyruvate carboxylase, catalyzes the reaction of GTP with oxaloacetate to produce GDP, phosphoenolpyruvate, and carbon dioxide. ITP can replace GTP as the phosphorylating substrate. 

This enzyme [EC 4.1.1.38] (also known as phosphoenolpyruvate carboxytransphosphorylase, phosphopyruvate carboxylase, and phosphoenolpyruvate carboxylase) catalyzes the reaction of phosphoenolpyruvate with orthophosphate and carbon dioxide to produce oxaloacetate and pyrophosphate (or diphosphate). The enzyme also catalyzes the reaction of phosphoenolpyruvate with orthophosphate to produce pyruvate and pyrophosphate. 

In gluconeogenesis, phosphopyruvate carboxylase permits the surmount of a thermodynamic hurdle and determines the conversion from oxaloacetate back to pyruvate, which can now enter the gluconeogenic stream, provided, of course, that the common steps for glycolysis and gluconeogenesis are placed on the gluconeogenic track. 

Mukerji,S.K. Four-hourly variations in the activities of malate dehydrogenase (decarboxy-lating) and phosphopyruvate carboxylase in the cactus (Nopalea dejecta) plant. Indian J. Biochem. 5,62-64 (1968)... 

Ballard, F. J., and Hopgood, M. F., 1973, Phosphopyruvate carboxylase induction by l-tryptophan. Effects on synthesis and degradation of the enzyme, Biochem. J. 136 259. 

Fig. 15.2 Pyruvate metabolism, gluconeogenesis and glycolysis. Key enzymes shown are 1, fructose 1-phosphate aldolase (EC 4.1.2.13) 2, fructose 1,6-bisphosphate aldolase (EC 4.1.2.13) 3, NAD rglyceraldehyde 3-phosphate dehydrogenase (EC 1.2.1.12) 4, 3-phosphoglycerate kinase (EC 2.T.2.3) 5, phosphoglyceromutase (EC 2.7.5.3) 6, phosphopyruvate hydratase (enolase) (EC 4.2.1.11) 7, pyruvate kinase (EC 2.7.1.40) 8, pyruvate carboxylase (EC 6.4.1.1) 9, phosphopyruvate carboxylase...

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