Glycine reductase protein C. Properties and characterization of its role in the reductive cleavage of Se-carboxymethyl-selenoprotein A.
The clostridial glycine reductase complex catalyzes the reductive deamination of glycine in an energy-conserving process that results in the esterification of orthophosphate. The complex consists of three protein components: selenoprotein A; protein B, a carbonyl group protein; and protein C, a sulfhydryl protein. The protein C component also catalyzes the arsenate-dependent decomposition of acetyl phosphate. Reaction of protein C with iodoacetate inhibits its ability to decompose acetyl phosphate, but this inactivation of the enzyme by alkylation is prevented in the presence of the substrate indicating the formation of an unreactive enzyme-bound acetylthiol ester. The Se-carboxy-methylselenocysteine residue of the selenoprotein A component of glycine reductase was generated by selective alkylation of the ionized selenol group at pH 6 with [14C]bromoacetate. Using this pure alkylated selenoprotein A as substrate, it was shown that protein C catalyzes the conversion of the [14C]carboxymethyl group, in selenoether linkage to protein A, to [14C]acetate in the presence of arsenate, dithiothreitol, and Mg2+. A procedure using hydrophobic chromatographic matrices was developed for the large scale isolation of protein C, and a number of the properties of the enzyme were determined.
Laboratory of Biochemistry, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
T C
TC
Stadtman
J N
JN
Davis
D000478:Alkylation; D000594:Amino Acid Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism*; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D001426:Bacterial Proteins / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003013:Clostridium / Q000201:enzymology; D007504:Iron Radioisotopes; D007700:Kinetics; D046911:Macromolecular Substances; D008962:Models, Theoretical; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000302:isolation & purification / Q000378:metabolism*; D012643:Selenium / Q000378:metabolism*; D012644:Selenium Radioisotopes; D051140:Selenoproteins
D000596:Amino Acids; D001426:Bacterial Proteins; D002250:Carbon Radioisotopes; D007504:Iron Radioisotopes; D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D012644:Selenium Radioisotopes; D051140:Selenoproteins; C054667:selenoprotein A; D000594:Amino Acid Oxidoreductases; C020815:glycine reductase; D012643:Selenium