Expression, purification, and characterization of galactose oxidase of Fusarium sambucinum in E. coli

A gene encoding a galactose oxidase (GalOx) was isolated from Fusarium sambucinum cultures and overexpressed in Escherichia coli yielding 4.4 mg enzyme per L of growth culture with a specific activity of 159 U mg−1. By adding a C-terminal His-tag the enzyme could be easily purified with a single affinity chromatography step with high recovery rate (90%). The enzyme showed a single band on SDS-PAGE with an apparent molecular mass of 68.5 kDa. The pH optimum for the oxidation of galactose was in the range of pH 6-7.5. Optimum temperature for the enzyme activity was 35 °C, with a half-life of 11.2 min, 5.3 min, and 2.7 min for incubation at 40 °C, 50 °C, and 60 °C, respectively. From all tested substrates, the highest relative activity was found for 1-methyl-β-galactopyranoside (226 U mg−1) and the highest catalytic efficiency (kcat/Km) for melibiose (2700 mM−1 s−1). The enzyme was highly specific for molecular oxygen as an electron acceptor, and showed no appreciable activity with a range of alternative acceptors investigated. Different chemicals were tested for their effect on GalOx activity. The activity was significantly reduced by EDTA, NaN3, and KCN.