title: Methemoglobin reduction mediated by D-amino acid dehydrogenase in Propsilocerus akamusi (Tokunaga) larvae.
abstract: A methemoglobin (metHb) reduction system is required for aerobic respiration. In humans, Fe(III)-heme-bearing metHb (the oxidized form of hemoglobin), which cannot bind oxygen, is converted to Fe(II)-heme-bearing oxyhemoglobin (oxyHb, the reduced form), which can bind oxygen, in a system comprising NADH, NADH-cytochrome b5 reductase, and cytochrome b5. However, the mechanism of metHb reduction in organisms that inhabit oxygen-deficient environments is unknown. In the coelomic fluid of the larvae of Propsilocerus akamusi, which inhabit a microaerobic environment, we found that metHb was reduced by D-alanine. We purified an FAD-containing enzyme, D-amino acid dehydrogenase (DAD), and component V hemoglobin from the larvae. Using the purified components and spectrophotometric analyses, we showed a novel function of DAD: DAD-mediation of P. akamusi component V metHb reduction with using D-alanine as an electron donor. P. akamusi larvae possess this D-alanine-DAD metHb reduction system in addition to a previously discovered NADH-NADH-cytochrome b5 reductase system. This is the first report of the presence of DAD in a multicellular organism. The molecular mass of DAD was estimated to be 45 kDa. The optimal pH and temperature of the enzyme were 7.4 and 20 °C, respectively, and the optimal substrate was D-alanine. The enzyme activity was inhibited by benzoate and sulfhydryl-binding reagents.
authors.affiliation: Department of Materials and Applied Chemistry, College of Science and Technology, Nihon University, Kanda-Surugadai, Chiyoda Ward, Tokyo 101-8308, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kobori
authors.affiliation: Department of Materials and Applied Chemistry, College of Science and Technology, Nihon University, Kanda-Surugadai, Chiyoda Ward, Tokyo 101-8308, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Tanigawa
authors.affiliation: Department of Materials and Applied Chemistry, College of Science and Technology, Nihon University, Kanda-Surugadai, Chiyoda Ward, Tokyo 101-8308, Japan.
authors.forename: Shintaro
authors.initials: S
authors.lastname: Maeda
authors.affiliation: Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hori
authors.affiliation: Department of Biochemistry, Faculty of Science, Okayama University of Science, Okayama 700-0005, Japan.
authors.forename: Toshitsugu
authors.initials: T
authors.lastname: Yubisui
authors.affiliation: Department of Materials and Applied Chemistry, College of Science and Technology, Nihon University, Kanda-Surugadai, Chiyoda Ward, Tokyo 101-8308, Japan. Electronic address: ocean_nagata@axel.ocn.ne.jp.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Nagata
mesh_terms: D000409:Alanine / Q000378:metabolism; D000818:Animals; D002683:Chironomidae / Q000378:metabolism*; D015786:Cytochromes b5 / Q000378:metabolism; D003605:D-Amino-Acid Oxidase / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007814:Larva / Q000378:metabolism; D008706:Methemoglobin / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D013696:Temperature
chemical_list: D008706:Methemoglobin; D015786:Cytochromes b5; D003605:D-Amino-Acid Oxidase; D000409:Alanine; D010100:Oxygen
keywords: Electron-transfer; Methemoglobin; Propsilocerus akamusi; d-Alanine; d-Amino acid dehydrogenase