Cellulose digestion in the wood-eating higher termite, Nasutitermes takasagoensis (Shiraki): distribution of cellulases and properties of endo-beta-1,4-glucanase.

beta-Glucosidase [EC 3.2.1.21] and endo-beta-1,4-glucanase [EC 3.2.1.4] activities were measured in the wood-eating higher termite Nasutitermes takasagoensis. beta-Glucosidase activity was present mainly in the salivary glands (66.7%) and midgut (22.2%), whereas endo-beta-1,4-glucanase activity was detected mainly in the midgut (90.1%). Specific activity of endo-beta-1,4-glucanase was also the highest in the midgut, indicating that cellulose is digested in the midgut. The major endo-beta-1,4-glucanase component of N. takasagoensis was purified from whole termites by gel filtration on Sephaoryl S-200 HR, Superdex-75 and hydroxyapatite column chromatography. Subsequently, the endo-beta-1,4-glucanase activity from a crude midgut extract was eluted in an identical volume (Kd = 0.68) to that from whole termites, suggesting the purified endo-beta-1,4-glucanase is identical to that in the midgut. The molecular weight of the purified endo-beta-1,4-glucanase was 47 kDa, and its specific activity was 1,200 units/mg. The optimal pH and temperature were 5.8 and 65 degrees C, respectively. The Km and Vmax values on carboxymethyl cellulose were 8.7 mg/ml and 2,222 units/mg, respectively. The purified endo-beta-1,4-glucanase hydrolyzed cellopentaose to cellotriose and cellobiose, and cellotetraose to cellobiose and a trace of cellotriose and glucose, but cellotriose and cellobiose were not hydrolyzed. The activity and stability on pH and temperature of the purified endo-beta-glucanase are prominent among those from various organisms.