A ‘blue’ copper oxidase from Nitrosomonas europaea

Abstract

A soluble copper-containing protein with p-phenylenediamine oxidase activity was purified from Nitrosomonas europaea by flat-bed isoelectric focusing and chromatography on Sephacryl S-300. The native and subunit molecular weights were 127 500 and 40 100, respectively; the isoelectric point was pH 4.63. The protein had an absorption maximum at 607 nm in the oxidized form with an extinction coefficient of 6.0 cm −1 · mM −1 at pH 7.5. On reduction with dithionite, the absorbance was abolished. The electron paramagnetic resonance spectrum of the protein showed evidence for both Type 1 and Type 2 copper in a 1:1 ratio. The protein catalyzed the aerobic oxidation of p-phenylenediamine, cytochrome c-554, and hydroxylamine oxidoreductase. The enzyme catalyzed the reduction of nitrite with cytochrome c-552 as electron donor. In contrast, p-phenylenediamine, reduced cytochrome c-554, and hydroxylamine oxidoreductase were not active as electron donors for nitrite reduction.