Production of thermostable α-galactosidase from thermophilic fungusHumicola sp

Abstract

The thermophilic fungus,Humicola sp isolated from soil, secreted extracellular α-galactosidase in a medium cotaining wheat bran extract and yeast extract. Maximum enzyme production was found in a medium containing 5% wheat bran extract as a carbon source and 0.5% beef extract as a carbon and nitrogen source. Enzyme secretion was strongly inhibited by the presence of Cu²⁺, Ni²⁺ and Hg²⁺ (1mM) 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° C to 55°C, with maximum activity (5.54 U ml⁻¹) at 45°C. Optimum pH and temperature for enzyme activity were 5.0 and 60° C respectively. One hundred per cent of the original activity was retained after heating the enzyme at 60°C for 1 h. At 5mM Hg²⁺ strongly inhibited enzyme activity. TheK _m andV _max forp-nitrophenyl-α-d-galactopyranoside were 60μM and 33.6 μmol min⁻¹ mg⁻¹, respectively, while for raffinose those values were 10.52 mM and 1.8 μmol min⁻¹ mg⁻¹, respectively.