Pyruvate carboxylase catalyzes the reaction of pyruvate, ATP, and bicarbonate to form oxaloacetate, ADP, and orthophosphate. The active form of the enzyme is a tetramer, with one molecule each of biotin and Mn++ associated with each protein monomer. The reaction requires Mg++. Acetyl CoA is an allosteric activator of pyruvate carboxylase; the reaction does not proceed to a significant extent in its absence (Keech and Utter 1963; Scrutton and Utter 1967; Jitrapakdee et al. 2002).