The mitochondrial glycine cleavage system. Purification and properties of glycine decarboxylase from chicken liver mitochondria.
Glycine decarboxylase, tentatively called P-protein and considered a constituent of the glycine cleavage system, was purified to apparent homogeneity from chicken liver mitochondria. P-protein is a homodimer having a Mr = approximately 200,000 and consisting of identical subunits with Mr = approximately 100,000. Each subunit appears to contain an equimolar pyridoxal 5'-phosphate which is bound to the protein, possibly through a protonated aldimine linkage. The isoelectric point of P-protein was 7.2. P-protein could bind glycine, showing a Kd of 33 mM for it, and could catalyze glycine decarboxylation even though the rate of decarboxylation catalyzed by P-protein alone was extremely low. The product of glycine decarboxylation was methylamine and the Km for glycine. Methylamine could bind to P-protein, giving a Kd value of 63 mM, and it inhibited the glycine decarboxylation. P-protein alone could also slightly catalyze the exchange of carboxyl carbon of glycine with CO2 and the exchange appeared to obey a ping-pong mechanism. Both glycine decarboxylation and the glycine-CO2 exchange catalyzed by P-protein were stimulated 100-fold or more by the addition of lipoic acid, which is a functional group of H-protein. We may define P-protein as glycine decarboxylase although P-protein alone exhibits only very low catalytic activities.
D000594:Amino Acid Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism*; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002645:Chickens; D005998:Glycine / Q000302:isolation & purification / Q000378:metabolism; D050961:Glycine Decarboxylase Complex H-Protein; D050841:Glycine Dehydrogenase (Decarboxylating); D007700:Kinetics; D046911:Macromolecular Substances; D008930:Mitochondria, Liver / Q000201:enzymology*; D008970:Molecular Weight; D011485:Protein Binding; D013053:Spectrophotometry
D000596:Amino Acids; D050961:Glycine Decarboxylase Complex H-Protein; D046911:Macromolecular Substances; D000594:Amino Acid Oxidoreductases; D050841:Glycine Dehydrogenase (Decarboxylating); D005998:Glycine