A constitutive, plasma-membrane bound β-glucosidase in Trichoderma reesei

Abstract

Plasma membranes of Trichoderma reesei QM 9414, isolated from protoplasts by means of the concanavalin A procedure, contained β-glucosidase activity, which appeared constitutively upon growth on glucose. The enzyme had a pH optimum around 6, and was active on p-nitrophenyl-β-d-glucoside, cellobiose and sophorose (Km 0.7, 3.9 and 3.1 mM, respectively). Glucose was only weakly inhibitory (Ki 7 mM). Treatment of the plasma membranes with Triton X-100, Tween 80 or digitonin solubilized more than 60% of the membrane-bound β-glucosidase activity. The enzyme so solubilized exhibited an Mr of 70 000 ± 5000 and an isoelectric point at pH 8.2 ± 0.3. © 1986.