Purification and characterization of a beta-galactosidase from Fusarium oxysporum var. lini.

Beta-D-Galactosidase was purified from a cellular extract of Fusarium oxysporum var. lini by heat shock and successive chromatography on DEAE-cellulose DE-52 and Sephadex G-100. The purified enzyme was homogeneous on SDS gel electrophoresis. It was inhibited by divalent cations such as Zn++, Mg++, and Ca++. The Michaelis constant and maximum velocity values for o-nitrophenyl beta-D-galacto-pyranoside were 6.76 mM and 816.7 mumol X mg protein-1 X min-1. The isoelectric point was 3.83, and the optimal pH and temperature were 5.0 and 55 degrees C. The estimated molecular weight of the enzyme was 224,000 by gel filtration and 36,300 by SDS-PAGE. The enzyme was considered a hexamer. o-Nitrophenyl-beta-D-galacto-pyranoside hydrolysis was activated by lactose, suggesting an allosteric nature of the enzyme.