title: Thyroxine-supported oxidation in the myeloperoxidase system.
abstract: Thyroxine and other iodothyronines (concentrations in the nanomolar range) stimulated the oxidation of NADH in the myeloperoxidase-H2O2-Cl- system. In the absence of chloride, thyroxine had only a marginal effect. This suggests that thyroxine increased the generation of chlorinating oxidants. A peroxidase-catalysed oxidation product of thyroxine, 3,5-diiodotyrosine, was inactive. Pre-incubation of thyroxine in the myeloperoxidase system showed that thyroxine was oxidized to a product capable of stimulating NADH oxidation. Reduction and alkylation of myeloperoxidase under nondenaturing conditions also increased the oxidative activity of the enzyme. It is postulated that both iodoacetamide and a thyroxine-derived oxidation product (presumably a quinone) alkylate sulphydryl groups near the active centre of myeloperoxidase making it more accessible for its substrate.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, University of Stellenbosch, Tygerberg, South Africa.
authors.forename: J M
authors.initials: JM
authors.lastname: van Zyl
authors.forename: B J
authors.initials: BJ
authors.lastname: van der Walt
authors.forename: A
authors.initials: A
authors.lastname: Kriegler
mesh_terms: D000478:Alkylation; D002712:Chlorides / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D007700:Kinetics; D009243:NAD / Q000378:metabolism*; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000378:metabolism*; D013974:Thyroxine / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D002712:Chlorides; D009243:NAD; D006861:Hydrogen Peroxide; D009195:Peroxidase; D013974:Thyroxine