title: Standard reduction potentials of all couples of the peroxidase cycle of lactoperoxidase.
abstract: Lactoperoxidase (LPO) is found in mucosal surfaces and exocrine secretions including milk, tears and saliva and has physiological significance in antimicrobial defense. Its predominant physiological role is to convert hydrogen peroxide and thiocyanate in hypothiocyanite. In this study, the standard reduction potentials of all redox couples involved in the halogenation and peroxidase cycle of LPO have been determined by multi-mixing stopped-flow spectroscopy. The standard reduction potentials of the redox couples compound I/native LPO, compound I/compound II of LPO, and compound II/native LPO are (1.09 +/- 0.01) V, (1.14 +/- 0.02) V, and (1.04 +/- 0.02) V, respectively, at pH 7 and 25 degrees C. Thus, for the first time, a full description of these important thermodynamic parameters of lactoperoxidase has been performed, allowing a better understanding in the substantial differences in the oxidation of two- and one-electron donors by LPO and other members of the mammalian heme peroxidase superfamily.
authors.affiliation: Department of Chemistry, Division of Biochemistry, BOKU--University of Natural Resources and Applied Life Sciences, Muthgasse 18, A-1190 Vienna, Austria.
authors.forename: Paul Georg
authors.initials: PG
authors.lastname: Furtmüller
authors.forename: Jürgen
authors.initials: J
authors.lastname: Arnhold
authors.forename: Walter
authors.initials: W
authors.lastname: Jantschko
authors.forename: Martina
authors.initials: M
authors.lastname: Zederbauer
authors.forename: Christa
authors.initials: C
authors.lastname: Jakopitsch
authors.forename: Christian
authors.initials: C
authors.lastname: Obinger
mesh_terms: D000818:Animals; D002417:Cattle; D007784:Lactoperoxidase / Q000737:chemistry* / Q000378:metabolism; D008892:Milk / Q000201:enzymology; D010084:Oxidation-Reduction
chemical_list: D007784:Lactoperoxidase