Characterization of a glucose 3-dehydrogenase from the cultivated mushroom(Agaricus bisporus)

An extracellular enzyme with glucose dehydrogenase activity was purified fr om liquid cultures of the basidiomycete Agaricus bisporus after growth with D-cellobiose or D-glucose as carbon source. The molecular mass was measure d as 57 kDa by gel filtration and 55 kDa by sodiumdodecyl sulphate/polyacry lamide gel electrophoresis, while the isoelectric point was at pH 3.6. By a nalysis of H-1-NMR spectra in D2O, the product of D-glucose oxidation was i dentified as 3-ketoglucose. The substrates oxidized included D-cellobiose, L-arabinose, D-xylose and sucrose, but the specificity parameter (k(cat)/K- m) was highest for D-glucose. Two electron accepters were identified, namel y 2,6-dichloroindophenol and p-benzoquinone. but reduction of dioxygen, fer ricyanide or cytochrome c was not detectable. The selective C-3 oxidation o f D-glucose is well-characterized for Agrobacterium and Flavobacterium, but this is the first report for a fungus.