title: Enzymological characterization of EpoA, a laccase-like phenol oxidase produced by Streptomyces griseus.
abstract: Laccase is an enzyme that catalyzes the oxidation of phenolic compounds by coupling the reduction of oxygen to water. While many laccases have been identified in plant and fungal species, enzymes of prokaryotic origin are poorly known. Here we report the enzymological characterization of EpoA, a laccase-like extracytoplasmic phenol oxidase produced by Streptomyces griseus. EpoA was expressed and purified with an Escherichia coli host-vector system as a recombinant protein fused with a C-terminal histidine-tag (rEpoA). Physicochemical analyses showed that rEpoA comprises a stable homotrimer containing all three types of copper (types 1-3). Various known laccase substrates were oxidized by rEpoA, while neither syringaldazine nor guaiacol served as substrates. Among the substrates examined, rEpoA most effectively oxidized N,N-dimethyl-p-phenylenediamine sulphate with a Km value of 0.42 mM. Several metal chelators caused marked inhibition of rEpoA activity, implying the presence of a metal center essential for the oxidase activity. The pH and temperature optima of rEpoA were 6.5 and 40 degrees C, respectively. The enzyme retained 40% activity after preincubation at 70 degrees C for 60 min. EpoA-like activities were detected in cell extracts of 8/40 environmental actinomycetes strains, which suggests that similar oxidases are widely distributed among this group of bacteria.
authors.affiliation: Life Science Research Center, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa 252-8510, Japan.
authors.forename: Kohki
authors.initials: K
authors.lastname: Endo
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Hayashi
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hibi
authors.forename: Kuniaki
authors.initials: K
authors.lastname: Hosono
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Beppu
authors.forename: Kenji
authors.initials: K
authors.lastname: Ueda
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017124:Conserved Sequence; D003300:Copper / Q000737:chemistry / Q000378:metabolism; D004125:Dimethyldithiocarbamate / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D042845:Laccase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010655:Phenylenediamines / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013053:Spectrophotometry / Q000379:methods; D013305:Streptomyces griseus / Q000201:enzymology*; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D004125:Dimethyldithiocarbamate; D004791:Enzyme Inhibitors; D010655:Phenylenediamines; D011506:Proteins; D011993:Recombinant Fusion Proteins; D003300:Copper; D042845:Laccase; D014442:Monophenol Monooxygenase