Effect of carbon source on the β-glucosidase system of the thermophilic fungus Humicola grisea.

H. grisea produced an extracellular β-glucosidase (EC 3.2.1.21) at high activity in media supplemented with carboxymethyl cellulose (CMC) or cellobiose. Cellobiose-induced β-glucosidase was insensitive to glucose repression whereas that of CMC-supplemented cultures was partially repressed. Molecular sieving revealed three main active components (Mr 50, 128 and 240 kDa). Glucose competitively inhibited β-glucosidase activities with Ki values of 0.9MM and 3.3MM (extracellular) and 10.2MM and 22.6MM (cytosolic), induced in the presence of CMC or cellobiose respectively.