Cellulases of Thermoascus aurantiacus (1979)
Type of ContentTheses / Dissertations
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
AuthorsTong, Chow Chinshow all
A β-glucosidase and three celulolytic enzymes designated as cellulase I, II and III have been purified from culture filtrates of Thermoascus aurantiacus. The enzymes were homogeneous in disc-gel electrophoresis. Data Obtained from gel filtration revealed their molecular weights to be 85,000 (β-glucosidase); 78,000 (cellulase I); 48,000 (cellulase II) and 34,000 (cellulase III): the carbohydrate content of these enzymes were 33.0, 5.5, 2.6 and 1.8% (w/w), respectively.
The β-glucosidase and the cellulases all showed a similar temperature optimum (approx. 70°c) and pH optimum (pH 4 . 5 - 5.0). When incubated at 65°C at their optimum pH for one hour, there was no loss of activity by any of these enzymes.
The three purified cellulases degraded native celluloses to different extents. Cellulase I was capable of acting on substrates with β-1,4 and mixed β- .1,3 ; β-1,6 linkages. Cellulase II had no activity on soluble CMC but was particularly active in hydrolysing insoluble celluloses with cellobiose as the primary product. On the other hand, cellulase III degraded soluble CMC most readily with the production of cellobiose and other oligosaccharides as products. β-glucosidase was active against p-nitrophenyl-β-D-glucoside and released glucose from cellobiose but had no hydrolysing ability on any form of cellulose. There was no synergism between the purified enzymes when tested on filter paper. The Km determined are as follows: 1.0 mg/ml (8-glucosidase on p-nitropheny l-β-D-glucoside); 8.8 mg/ml (cellulase I on CMC); 34.4 mg/ml (cellulase II on filter paper) and 4.6 mg/ml (cellulase III on CMC).
The mode of action of cellulase III on cellulase III on cellulodextrins and reduced cellulodextrins was examined. From the kinetic data and an analysis of the products, it is proposed that the specificity region of this enzyme is at least five glucose units in length.
These studies indicate that cellulase II is an exo-β-1,4-glucan cellobiosyl hydrolase; cellulase III, an exo-8-1,4-glucanase and 8-glucosidase, a cellulase-free cellobiase.