title: Kinetic behavior of the monodehydroascorbate radical studied by pulse radiolysis.
abstract: The reactions of the monodehydroascorbate radical (As.-) with various biological molecules were investigated by pulse radiolysis. As.- reacted with both fully reduced and semiquinone forms of hepatic NADH-cytochrome b5 reductase with second-order rate constants of 4.3 x 10(6) and 3.7 x 10(5) M-1 s-1, respectively, at pH 7.0. In contrast, no reaction of As.- with ferrous cytochrome b5 could be detected by pulse radiolysis, whereas the oxidation of cytochrome b5 by As.- was observed by ascorbate-ascorbate oxidase method. This suggests that the rate constant of As.- with the ferrous cytochrome b5 must be several orders in magnitude smaller than that of the disproportionation of As.-. On the other hand, As.- reduced Fe3+EDTA with a second-order rate constant of 4.0 x 10(6) M-1 s-1 but did not reduce ferric hemoproteins such as metmyoglobin, methemoglobin, and cytochrome b5 by either the pulse radiolysis or the ascorbate-ascorbate oxidase method.
authors.affiliation: Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Harada
authors.forename: K
authors.initials: K
authors.lastname: Hayashi
mesh_terms: D000818:Animals; D016227:Benzoquinones / Q000737:chemistry; D003579:Cytochrome Reductases / Q000737:chemistry; D042966:Cytochrome-B(5) Reductase; D003683:Dehydroascorbic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D005609:Free Radicals; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D011675:Pulse Radiolysis; D013552:Swine
chemical_list: D016227:Benzoquinones; D005296:Ferrous Compounds; D005609:Free Radicals; C025232:semiquinone radicals; C000820:semidehydroascorbic acid; D003579:Cytochrome Reductases; D042966:Cytochrome-B(5) Reductase; D003683:Dehydroascorbic Acid