PRODUCTION OF THERMOSTABLE ALPHA-GALACTOSIDASE FROM THERMOPHILIC FUNGUS HUMICOLA SP

The thermophilic fungus, Humicola sp isolated from soil, secreted extr acellular alpha-galactosidase in a medium containing wheat bran extrac t and yeast extract. Maximum enzyme production was found in a medium c ontaining 5% wheat bran extract as a carbon source and 0.5% beef extra ct as a carbon and nitrogen source. Enzyme secretion was strongly inhi bited by the presence of Cu2+ Ni2+ and Hg2+ (1 mM) in the fermentation medium. Production of enzyme under stationary conditions resulted in 10-fold higher activity than under shaking conditions. The temperature range for production of the enzyme was 37 degrees C to 55 degrees C, with maximum activity (5.54 U ml(-1)) at 45 degrees C. Optimum pH and temperature for enzyme activity were 5.0 and 60 degrees C, respectivel y. One hundred per cent of the original activity was retained after he ating the enzyme at 60 degrees C for 1 h. At 5 mM Hg2+ strongly inhibi ted enzyme activity. The K-m and V-max for p-nitrophenyl-alpha-D-galac topyranoside were 60 mu M and 33.6 mu mol min(-1) mg(-1), respectively , while for raffinose those values were 10.52 mM and 1.8 mu mol min(-1 ) mg(-1), respectively.