Abstract
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 flavin-sulfite complex. The approximately 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 K(m) 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.
Highlights
From the Department of Structural and Functional Biology, University of Insubria, via J
The 450-nm band exhibited a shoulder of ϳ470 nm that was similar to the resolved 450-nm band observed for free flavins in non-polar solvents [19] and similar to the spectrum of monomeric sarcosine oxidase (MSOX) [20] and R. gracilis D-amino-acid oxidase (DAAO) [21]
The results reported in the present work indicate that the recombinant Glycine oxidase (GO) from B. subtilis is a flavoenzyme containing 1 mol of a non-covalently bound FAD/45-kDa protein monomer
Summary
DAAO (containing 1 mole of non-covalently bound FAD per 40 kDa monomer) catalyzes the oxidative deamination of neutral and (with a lower efficiency) basic D-amino acids to give the corresponding ␣-keto acids, ammonia and hydrogen peroxide [4]. TSOXs use tetrahydrofolate as a substrate, and, in this regard, they resemble mammalian SDH and DMGDH [7] In mammals, these two enzymes catalyze the oxidative demethylation of sarcosine in the mitochondria. These two enzymes catalyze the oxidative demethylation of sarcosine in the mitochondria They are monomeric enzymes (97 and 96 kDa, respectively) containing a single, covalently bound flavin and are considered to be the two main folate-containing enzymes in rat liver mitochondria. These enzymes are linked to the electron transport chain and form 5,10-methylenetetrahydrofolate [8]
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