Components of termite and protozoal cellulases from the lower termite, Coptotermes lacteus froggatt

Abstract

The cellulase produced by the termite Coptotermes lacteus consists of two main components. One component is a β-1,4-glucosidase (EC 3.2.1.21) (M r in the range 2–4 × 10 6) which is active predominantly against cellobiose. This activity is completely inhibited by 30 mM glucono-δ-lactone and is thus true cellobiase activity. It has little effect on crystalline cellulose and is not active against carboxymethyl cellulose (CMC). Aggregate forms of the β-1,4-glucosidase ranging from monomeric to tetrameric can be seen by electron microscopy. The second component, an endo-β-1,4-glucanase (EC 3.2.1.4), is active against CMC with no activity against crystalline cellulose. The main products formed from CMC are cellotriose and cellobiose. A minor component, an exo-β-1,4-glucosidase (EC 3.2.1.74) is also present. The cellulase(s) from the paunch, which contains three species of Protozoa, can be separated into five components on Superose 6B. The first two eluted are β-1,4-glucosidases (EC 3.2.1.21); their cellobiase activity is inhibited by glucono-δ-lactone. They are inactive against crystalline cellulose or CMC. The next two components eluted are endo-β-1,4-glucanases (EC 3.2.1.4) as their major hydrolytic activity is against CMC. Glucose is produced in significant amounts from CMC by both components, one of which also hydrolyses cellobiose but this activity is not inhibited by glucono-δ-lactone. The last component eluted is an exo-β-1,4-glucosidase (EC 3.2.1.74) as its major activity is to produce glucose from crystalline cellulose. Its cellobiase activity is not inhibited by glucono-δ-lactone.