Glycine oxidase from Bacillus subtilis - Characterization of a new flavoprotein

Glycine oxidase (GO) is a homotetrameric flavoenzyme that contains one molecule of non-covalently bound flavin adenine dinucleotide per 47 kDa protein monomer. GO is active on various amines (sarcosine, N-ethylglycine, glycine) and D-amino acids (D-alanine, D-proline). The products of GO reaction with various substrates have been determined, and it has been clearly shown that GO catalyzes the oxidative deamination of primary and secondary amines, a reaction similar to that of D-amino acid oxidase, although its sequence homology is higher with enzymes such as sarcosine oxidase and N-methyltryptophane oxidase. GO shows properties that are characteristic of the oxidase class of flavoproteins: it stabilizes the anionic flavin semiquinone and forms a reversible covalent flavinsulfite complex. The -300 mV separation between the two FAD redox potentials is in accordance with the high amount of the anionic semiquinone formed on photoreduction. GO can be distinguished from D-amino acid oxidase by its low catalytic efficiency and high apparent Km value for D-alanine. A number of active site ligands have been identified; the tightest binding is observed with glycolate, which acts as a competitive inhibitor with respect to sarcosine. The presence of a carboxylic group and an amino group on the substrate molecule is not mandatory for binding and catalysis.