SEARCH Articles Figures Tables Pyruvate carboxylase reaction. Pyruvate carboxylase adds a carboxyl group from bicarbonate to pyruvate to form oxaloacetate. Biotin is used to activate and transfer the CO2. The energy to form the covalent biotin-C02 complex is provided by the high-energy phosphate bond of ATP, which is cleaved in the reaction. The enzyme is activated by acetyl CoA. [Publishers Imprint]