"Pyruvate Carboxylase, Structure and Function".

Pyruvate carboxylase is a metabolic enzyme that fuels the tricarboxylic acid cycle with one of its intermediates and also participates in the first step of gluconeogenesis. This large enzyme is multifunctional, and each subunit contains two active sites that catalyze two consecutive reactions that lead to the carboxylation of pyruvate into oxaloacetate, and a binding site for acetyl-CoA, an allosteric regulator of the enzyme. Pyruvate carboxylase oligomers arrange in tetramers and covalently attached biotins mediate the transfer of carboxyl groups between distant active sites. In this chapter, some of the recent findings on pyruvate carboxylase functioning are presented, with special focus on the structural studies of the full length enzyme. The emerging picture reveals large movements of domains that even change the overall quaternary organization of pyruvate carboxylase tetramers during catalysis.