Glycine Metabolism

Abstract

Abstract The electron carrier protein (P2) from Peptococcus glycinophilus, coupling the pyridoxal phosphate-related decarboxylation of glycine to the flavin adenine dinucleotide-mediated electron transfer to diphosphopyridine nucleotide, has been purified to homogeneity. Estimation of the molecular weight by sodium dodecyl sulfate acrylamide gel electrophoresis and by use of Sephadex G-100 gave values of approximately 12,600. The value based on amino acid residues is between 12,010 and 12,600. The protein contains 1 cysteine residue and 1 lipoic acid residue per molecule. Slight tendency for the monomeric form to aggregate into a tetramer having a molecular weight of over 48,000 was observed, but could be prevented by the addition of mercaptoethanol to the preparation. The electron transfer system exhibits high specificity for lipoate derivatives, i.e. α-lipoate, lipoyllysine, or lipoamide with the analogues 1,3-dimercaptopropanol, 1,2-dimercaptopropanol, and dithiothreitol being ineffective electron donors. Thioredoxin from Escherichia coli was unable to substitute for P2 in either the glycine decarboxylation-CO2 exchange reaction or in the electron transfer reaction.