PRODUCTION OF CELLULASES BY ASPERGILLUS-FUMIGATUS AND CHARACTERIZATION OF ONE BETA-GLUCOSIDASE

Aspergillus fumigatus produces substantial extracellular cellulases on several cellulosic substrates including simple sugars. Low glucose po tentiates enzyme production, but most cellulose-induced cellulases are repressed by high glucose. As production of cellulase in a wide subst rate range is unusual, the cellulolytic complex of this thermophilic f ungus was investigated. A beta-glucosidase was separated by gel filtra tion and ion-exchange chromatography. It migrated in native polyacryla mide gel as a single protein (130 kDa), which split under denaturing c onditions into two smaller proteins having molecular masses of 90 kDa and 45 kDa. However, only the 90-kDa protein was active. Conventional chromatographic procedures were unsuccessful for the separation of the se two proteins. Therefore, the 130-kDa protein was studied for its ki netic properties. It hydrolyzed p-nitrophenyl-beta-D-glucopyranoside ( p-NPG) and cellobiose, but not beta-glucans, laminarin, and p-nitrophe nyl-beta-D-xilopyranoside. The optimal pH and temperature of p-NPG and cellobiose hydrolysis were 5.0 and 4.0, and 65 degrees C and 60 degre es C, respectively. The K-m values, determined for cellobiose and p-NP G of hydrolysis, were 0.075 mM and 1.36 mM, respectively. Glucose comp etitively inhibited the hydrolysis of p-NPG. The K-i was 3.5 mM.