title: Reduction of ferric haemoproteins by tetrahydropterins: a kinetic study.
abstract: We previously showed that one-electron transfer from tetrahydropterins to iron porphyrins is a very general reaction, with formation of an intermediate cation radical similar to the one detected in NO synthase. As a model reaction, the rates of reduction of eight haemoproteins by diMePH4 (6,7-dimethyltetrahydropterin) have been studied and correlated with their one-electron reduction potentials, E(m) (Fe(III)/Fe(II)). On the basis of kinetic data analyses, a bimolecular collisional mechanism is proposed for the electron transfer from diMePH4 to ferrihaemoproteins. Haemoproteins with reduction potentials below -160 mV were shown not to be reduced by diMePH4 to the corresponding ferrohaemoproteins. For haemoproteins with reduction potentials more positive than -160 mV, such as chloroperoxidase, cytochrome b5, methaemoglobin and cytochrome c, there was a good correlation between the second-order reduction rate constant and the redox potential, E(m) (Fe(III)/Fe(II)): [formula: see text]. The rate of reduction of cytochrome c by BH4 [(6R)-5,6,7,8-tetrahydrobiopterin] was determined to be similar to that of the reduction of cytochrome c by diMePH4. These results confirm the role of tetrahydropterins as one-electron donors to Fe(III) porphyrins.
authors.affiliation: Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques (CNRS UMR 8601), Université Paris 5, 45 rue des Saints Pères, 75270 Paris Cedex 06, France. Chantal.Capeillere-Blandin@univ-paris5.fr
authors.forename: Chantal
authors.initials: C
authors.lastname: Capeillere-Blandin
authors.forename: Delphine
authors.initials: D
authors.lastname: Mathieu
authors.forename: Daniel
authors.initials: D
authors.lastname: Mansuy
mesh_terms: D002711:Chloride Peroxidase / Q000737:chemistry / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000378:metabolism; D000072467:Cytochrome P450 Family 2; D015786:Cytochromes b5 / Q000737:chemistry / Q000378:metabolism; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D006420:Hemeproteins / Q000737:chemistry* / Q000378:metabolism*; D006735:Horseradish Peroxidase / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008706:Methemoglobin / Q000737:chemistry / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D010544:Peroxidases / Q000737:chemistry / Q000378:metabolism; D011622:Pterins / Q000737:chemistry* / Q000494:pharmacology*; D013255:Steroid 21-Hydroxylase / Q000737:chemistry / Q000378:metabolism
chemical_list: C508555:6,7-dimethyltetrahydropterin; D005290:Ferric Compounds; D006420:Hemeproteins; D011622:Pterins; D045304:Cytochromes c; D008706:Methemoglobin; D015786:Cytochromes b5; D003577:Cytochrome P-450 Enzyme System; D006735:Horseradish Peroxidase; D010544:Peroxidases; C021799:microperoxidase; D002711:Chloride Peroxidase; D019001:Nitric Oxide Synthase; C065407:CYP2C5 protein, Oryctolagus cuniculus; D000072467:Cytochrome P450 Family 2; D013255:Steroid 21-Hydroxylase