Glycine metabolism by rat liver mitochondria. Reconstruction of the reversible glycine cleavage system with partially purified protein components

An enzyme system which catalyzes the degradation of glycine to one carbon unit, ammonia, and carbon dioxide and the synthesis of glycine from these three substances has been isolated from rat liver mitochondria. The reversible glycine cleavage system is composed of four protein components named as P-, H-, L-, and T-protein, respectively. A procedure is described for the purification of P-protein which catalyzes the decarboxylation of glycine or its reverse reaction in the presence of H-protein, and for T-protein which participates in the formation of one carbon unit and ammonia or the reverse reaction. The procedure described leads to the isolation of a nearly homogeneous form of T-protein but P-protein still is heterogeneous. The molecular weight of T-protein, estimated by molecular sieve chromatography, is 33,000. Properties of the synthesis and cleavage reactions and the exchange of carboxyl group of glycine with bicarbonate are also presented.