title: Ascorbate regeneration by the reduced form of 2-amino-3-carboxy-1, 4-naphthoquinone, a strong growth stimulator for bifidobacteria.
abstract: Nonenzymatic reduction of dehydroascorbate into ascorbate by the reduced form (quinol form) of 2-amino-3-carboxy-1,4-naphthoquinone, a strong growth stimulator for bifidobacteria, has been found. The bimolecular reaction rate constant was evaluated as 9 M(-)(1) s(-)(1) at pH 7.0. This reaction has been successfully coupled with enzymatic regeneration of the naphthoquinol by NAD(P)H in cell-free extracts of Bifidobacterium longum 6001. The overall reaction is a regeneration of NAD(P)(+) by dehydroascorbate [or a regeneration of ascorbate by NAD(P)H], in which the naphthoquinone/quinol redox couple functions as an electron transfer mediator. Kinetic study of the reduction of dehydroascorbate with related quinol compounds suggested the significance of the amino substituent of the naphthoquinol. A mechanism of the electron transfer from the quinol to dehydroascorbate is proposed, where the first step of the reaction is a nucleophilic addition of the C(2)-amino substituent of the naphthoquinol to the C(2)-position of dehydroascorbate to form a Schiff base intermediate.
authors.affiliation: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Yamazaki
authors.forename: K
authors.initials: K
authors.lastname: Iwasa
authors.forename: K
authors.initials: K
authors.lastname: Kano
authors.forename: T
authors.initials: T
authors.lastname: Ikeda
authors.forename: N
authors.initials: N
authors.lastname: Taketomo
authors.forename: T
authors.initials: T
authors.lastname: Kaneko
mesh_terms: D001205:Ascorbic Acid / Q000737:chemistry*; D001644:Bifidobacterium / Q000187:drug effects* / Q000254:growth & development; D003683:Dehydroascorbic Acid / Q000737:chemistry*; D006133:Growth Substances / Q000737:chemistry / Q000494:pharmacology*; D009249:NADP / Q000737:chemistry; D009285:Naphthoquinones / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology*; D010084:Oxidation-Reduction; D011424:Propionibacterium / Q000737:chemistry
chemical_list: C108806:2-amino-3-carboxy-1,4-naphthoquinone; D006133:Growth Substances; D009285:Naphthoquinones; D009249:NADP; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid