Alcohol oxidase catalyzes the oxidation of short lines alcohol to aldehyde. In this study, alcohol oxidase from Hansenula polymorpha (HpAOD) was induced by addition of 0.5% methanol as the carbon source and purified to electrophoretic homogeneity by column chromatographies. The purified HpAOD was immobilized with DEAE-cellulose particles and its biochemical properties were compared with those of free enzyme. The substrate specificity and the optimum pH of immobilized enzyme were similar to those of free enzyme. On the other hand, the Km values of free and immobilized enzymes for ethanol were 6.66 and 14.65 mM, respectively. The optimum temperature for free enzyme was 50°C, whereas that for immobilized enzyme was 65°C. Immobilized enzyme showed high stability against long storage. Immobilized enzyme was also tested for the enzymatic determination of ethanol by the colorimetric method. We detected 1 mg/liter ethanol (1×10 -4 % ethanol) by 2,6-dichloroindophenol system. Therefore, the present study demonstrated that immobilized HpAOD has high substrate specificity toward ethanol and storage stability, which may be of considerable interest for alcohol biosensor and industrial application.
A gene (PH0311) encoding a hypothetical protein from the genome sequence data of the hyperthermophilic archaeon Pyrococcus horikoshii OT3 was cloned and over-expressed in Escherichia coli. The purified recombinant protein was found to possess FAD-dependent NADH oxidase activity, although it lacked sequence homology to any other known general NADH oxidase family. The product of the PH0311 gene was thus designated PhNOX (NADH oxidase from Pyrococcus horikoshii), with an estimated molecular weight of 84 kDa by gel filtration and 22 kDa by SDS-PAGE, indicating it to be a homotetramer of 22 kDa subunits. PhNOX catalyzed the oxidation of reduced β-NADH with subsequent formation of H2O2 in the presence of FAD as a cofactor, but not α-NADH, α-NADPH, or β-NADPH. PhNOX showed high affinity for β-NADH with a Km value of 3.70 µΜ and exhibited optimum activity at pH 8.0 and 95 o C as it is highly stable against high temperature.
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