Carboxylation of pyruvate via extramitochondrial malic enzyme in rat skeletal muscle

Soluble rat skeletal muscle extract incubated in the presence of pyruvate, NaH14CO3, MgCl2 and NADP-generating system fixed H14CO3- at the rate of about 2.3 nmol/min per mg protein. The omission of pyruvate or NADPH-generating system abolished completely the fixation of H14CO3-. This suggests that malic enzyme is responsible for the carboxylation of pyruvate. A possible role of pyruvate carboxylation by extramitochondrial malic enzyme in the conversion of lactate into glycogen in skeletal muscle is discussed.