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J. Biochem, 2003, Vol. 133, No. 5 671-677
© 2003 Japanese Biochemical Society

BIOCHEMISTRY

Enzymological Characterization of EpoA, a Laccase-Like Phenol Oxidase Produced by Streptomyces griseus

Kohki Endo, Yutaka Hayashi, Takahiro Hibi, Kuniaki Hosono, Teruhiko Beppu and Kenji Ueda+,

Life Science Research Center, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa 252-8510

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°C, respectively. The enzyme retained 40% activity after preincubation at 70°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.

+ To whom correspondence should be addressed. Tel: +81-466-84-3936, Fax: +81-466-84-3935, E-mail: ueda{at}brs.nihon-u.ac.jp


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