title: Kinetic properties of light-dependent ascorbic acid oxidation by melanin.
abstract: The kinetic properties of ascorbic acid oxidation by light-activated melanin granules demonstrate the presence of a specific reactive site on the melanin granule saturable by ascorbic acid. Increased light intensity increased the Vmax and reduced the Km of this reaction, indicating increased affinity of the active site for ascorbic acid. The kinetics of this reaction are not markedly changed in a reduced-oxygen environment. Ascorbic acid oxidation is competitively inhibited by isoascorbic acid, an epimer of ascorbic acid, while other tested reducing agents are inactive. The Ki for isoascorbic acid is 1 mM, about the same as the Km of ascorbic acid.
authors.affiliation: Department of Ophthalmology, University of Texas Health Science Center at San Antonio 78284-6230.
authors.forename: R D
authors.initials: RD
authors.lastname: Glickman
authors.forename: R
authors.initials: R
authors.lastname: Sowell
authors.forename: K W
authors.initials: KW
authors.lastname: Lam
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism*; D002417:Cattle; D005609:Free Radicals; D007700:Kinetics; D008027:Light; D008543:Melanins / Q000378:metabolism*; D010084:Oxidation-Reduction; D010857:Pigment Epithelium of Eye / Q000378:metabolism
chemical_list: D005609:Free Radicals; D008543:Melanins; D001205:Ascorbic Acid