title: Iodide oxidation by a novel multicopper oxidase from the alphaproteobacterium strain Q-1.
abstract: Alphaproteobacterium strain Q-1 is able to oxidize iodide (I(-)) to molecular iodine (I(2)) by an oxidase-like enzyme. One of the two isoforms of the iodide-oxidizing enzyme (IOE-II) produced by this strain was excised from a native polyacrylamide gel, eluted, and purified. IOE-II appeared as a single band (51 kDa) and showed significant in-gel iodide-oxidizing activity in sodium dodecyl sulfate-polyacrylamide gel electrophoresis without heat treatment. However, at least two bands with much higher molecular masses (150 and 230 kDa) were observed with heat treatment (95°C, 3 min). IOE-II was inhibited by NaN(3), KCN, EDTA, and a copper chelator, o-phenanthroline. In addition to iodide, IOE-II showed significant activities toward phenolic compounds such as syringaldazine, 2,6-dimethoxy phenol, and p-phenylenediamine. IOE-II contained copper atoms as prosthetic groups and had UV/VIS absorption peaks at 320 and 590 nm. Comparison of several internal amino acid sequences obtained from trypsin-digested IOE-II with a draft genome sequence of strain Q-1 revealed that the products of two open reading frames (IoxA and IoxC), with predicted molecular masses of 62 and 71 kDa, are involved in iodide oxidation. Furthermore, subsequent tandem mass spectrometric analysis repeatedly detected peptides from IoxA and IoxC with high sequence coverage (32 to 40%). IoxA showed homology with the family of multicopper oxidases and included four copper-binding regions that are highly conserved among various multicopper oxidases. These results suggest that IOE-II is a multicopper oxidase and that it may occur as a multimeric complex in which at least two proteins (IoxA and IoxC) are associated.
authors.affiliation: Graduate School of Horticulture, Chiba University, Matsudo City, Chiba, Japan.
authors.forename: Mio
authors.initials: M
authors.lastname: Suzuki
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Eda
authors.forename: Shiaki
authors.initials: S
authors.lastname: Ohsawa
authors.forename: Yu
authors.initials: Y
authors.lastname: Kanesaki
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Yoshikawa
authors.forename: Kan
authors.initials: K
authors.lastname: Tanaka
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Muramatsu
authors.forename: Jun
authors.initials: J
authors.lastname: Yoshikawa
authors.forename: Ikuo
authors.initials: I
authors.lastname: Sato
authors.forename: Takaaki
authors.initials: T
authors.lastname: Fujii
authors.forename: Seigo
authors.initials: S
authors.lastname: Amachi
mesh_terms: D020561:Alphaproteobacteria / Q000145:classification / Q000201:enzymology* / Q000235:genetics; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D003300:Copper / Q000378:metabolism; D007454:Iodides / Q000378:metabolism*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010802:Phylogeny; D055503:Protein Multimerization; D017422:Sequence Analysis, DNA; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D007454:Iodides; D003300:Copper; D010088:Oxidoreductases; C024748:copper oxidase