On the Substrate Specificity and Some Properties of the Extracellular Oxidase from the Neonothopanus nambi Basidiomycete

The present study reports experimental data on substrate specificity and some properties of the extracellular enzyme with oxidase activity isolated from the mycelium of the higher fungus Neonothopanus nambi IBSO 2391 by treating the biomass with
-glucosidase. Gel-filtration chromatography showed that molecular weight of the isolated enzyme was 80 kDa. Spectral analysis did not reveal any chromophore components in the enzyme. The extracellular oxidase of the basidiomycete N. nambi IBSO 2391 was active with most of the aromatic compounds chosen as model substrates. An important fact is that the enzyme exhibited catalytic activity with no hydrogen peroxide or any other mediators added to the reaction mixture. The highest activity of the enzyme was observed in reactions with veratryl alcohol and hydroquinone. In reactions with guaiacol and aromatic amines (diaminobenzidine, o-dianisidine), the level of activity of the extracellular oxidase was considerably lower – by a factor of 2.5–3.5. In reactions with resorcinol, phenol, and caffeic acid, the catalytic efficiency of the enzyme was no greater than 6% of its activity with veratryl alcohol. Kinetic parameters of enzymatic reactions were determined for the most efficiently oxidized substrates. The addition of the chelating agent of divalent metal ions (EDTA) did not affect the activity of the extracellular oxidase from the fungus N. nambi IBSO 2391, indicating the absence of divalent metal ions in the molecule of the enzyme. At the same time, addition of the SH reagent (DTT) increased catalytic efficiency of the enzyme. The study showed that the extracellular oxidase of the fungus N. nambi IBSO 2391 functions in wide ranges of temperature and pH of the reaction medium, showing the highest catalytic activity at temperatures between 22 and 35 °C and pH 6.0. Results obtained in the current study provide the basis for studying potential uses of the isolated enzyme in biomedical analytics and bioremediation.