Thermostable β-xylosidase from Thermomonospora curvata

Thermomonospora curvata

produced a thermostable β-xylosidase during growth on birch xylan. The enzyme, extracted by sonication of early stationary phase mycelia, was purified by isoelectric focusing and size exclusion HPLC. The isoelectric point was pH 4.8. The molecular weight was estimated to be 102 000 by size exclusion HPLC and 112 000 by SDS-PAGE. Maximal activity occurred at pH 6–7 and 60–68°C. K _m values for xylobiose and p-nitrophenyl-β -D-xylopyranoside were 4.0 M and 0.6 M respectively. The enzyme was sensitive to low levels of Hg²⁺ (50% inhibition at 0.2 μM), but was stimulated by Co²⁺ and Pb²⁺. Addition of the xylosidase to a xylanase reaction mixture increased the liberation of xylose equivalents from xylan and decreased the proportion of xylobiose in the hydrolysate.