Purification and characterization of formate oxidase from a formaldehyde-resistant fungus

A formate oxidase activity was found in the crude extract of a formaldehyde-resistant fungus isolated from soil. The fungus was classified and designated as Aspergillus nomius IRI013, which could grow on a medium containing up to 0.45% formaldehyde and consumed formaldehyde completely. The specific activity of formate oxidase in the extract of the fungus grown on formaldehyde was found to be considerably higher than that in the extracts of the fungus grown on formate and methanol. Formate oxidase from the fungus grown on formaldehyde was purified to homogeneity. The enzyme had a relative molecular mass of 100000 and was composed of two apparently identical subunits that had a relative molecular mass of 59000. The enzyme showed the highest activity using formate as substrate. Hydrogen peroxide was formed during the oxidation of formate. The Michaelis constant for formate was 15.9 mM; highest enzyme activity was found at pH 4.5-5.0. The enzyme activity was strongly inhibited by NaN(3), p-chloromercuribenzoate and HgCl(2).