Isolation and characterization of glycolic acid oxidase from human liver

Glycolic acid oxidase has been isolated from human liver and purified over 3000-fold to a specific activity of 123 U/mg protein by a 5-step procedure. The preparation gave a single protein band on polyacrylamide gel electrophoresis, required flavin mononucleotide for catalytic activity, had a pH optimum between 8.2-8.8 depending on the substrate, and had a molecular weight of 105 000. The enzyme has a broad specificity towards alpha-hydroxy acids. Glycolate (Km = 3.3 . 10(-4) M) was the most effective substrate. The enzyme was stable for several months when stored as an (NH4)2SO4 precipitate or in 15% glycerol. Since glycolate inhibits the oxidation of glyoxylate to oxalate by glycolic acid oxidase, it is suggested that glycolic acid oxidase contributes to the synthesis of oxalate in vivo when the glyoxylate concentration is high and the glycolate concentration is low.