L-gulonolactone oxidase

L-gulonolactone oxidase (EC 1.1.3.8) is an enzyme that produces vitamin C, but is non-functional in Haplorrhini (including humans), in some bats, and in guinea pigs. It catalyzes the reaction of L-gulono-1,4-lactone with oxygen to L-xylo-hex-3-gulonolactone and hydrogen peroxide. It uses FAD as a cofactor. The L-xylo-hex-3-gulonolactone (2-keto-gulono-gamma-lactone) is able to convert to hexuronic acid (ascorbic acid) spontaneously, without enzymatic action.