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Pyruvate Carboxylase

1984; Academic Press; Linguagem: Inglês

10.1016/b978-0-12-152823-2.50005-2

0070-2137

Paul V. Attwood, D.B. Keech,

Enzyme Structure and Function

This chapter describes the structure of pyruvate carboxylase and the mechanism of its action. It also describes the carboxylation of biotin and pyruvate, the translocation of biotin between the two subsites, and the participation of the allosteric activator acetyl-CoA. Pyruvate carboxylase catalyzes the carboxylation of pyruvate to form oxaloacetate with the concurrent cleavage of MgATP to form MgADP and Pi. Along with other biotin-dependent enzymes, the active center of pyruvate carboxylase is believed to consist of two separate subsites with the covalently bound biotin acting as a mobile carboxyl-group carrier, shifting the activated carboxyl group from one subsite to the other. This idea of a flexible, covalently bound molecule providing a carboxyl-group shuttle system is not without precedent. For example, lipoic acid, the prosthetic group of dihydrolipoamide acetyl transferase, has been postulated to transfer acetyl groups in the pyruvate dehydrogenase complex, while pantetheine 4'-phosphate has been assigned a similar function in the acyl-carrier protein complex of the fatty acid-synthesizing complex in yeast. The basic difference between the latter two examples and the biotin-dependent enzymes is that lipoic acid and pantetheine shuttle activated groups between different enzymes within a multienzyme complex, whereas biotin acts as a carrier system between the subsites of a single active center.