1,3-beta-D-glucanases from Pisum sativum seedlings. II. Substrate specificities and enzymic action patterns

Abstract

Two purified pea 1,3-beta-D-glucanases (EC 3.2.1.6) hydrolyse laminarin (degree of polymerization 20), laminaridextrins (degree of polymerization 3--7), and their reduced 3H-derivatives, 1,3-beta-D-glucans which are partially substituted (carboxymethyl-pachyman) or crystalline (curdlan), and mixed-linkage beta-glucans. Enzyme kinetics and product-formation indicate endo-hydrolase activity with weak transglycosylase capacity. The enzymes do not hydrolyse beta-glucosides, the 1,3 linkage adjacent to the reducing end of chains, or cellulose and its derivatives. They degrade mixed-linkage beta-glucans, in a manner similar to Rhizopus arrhizus endo-1,3-beta-D-glucanase, to form the products expected from hydrolysis of linkages adjacent to 1,3-beta linkages. With respect to action patterns, glucanase I (from apical growing tissue) differs from glucanase II (from basal maturing tissue) in several respects: (a) on a molar basis, I generates reducing groups from all substances more rapidly than II; (b) lower laminaridextrins are hydrolysed by I at the non-reducing terminal linkage, while II preferentially hydrolyses internal linkages; (c) laminarin is hydrolysed to lower laminaridextrins by I more rapidly than II, but I takes longer than II to completely degrade laminarin chains; (d) the enzymes are differentially sensitive to different classes of non-competitive inhibitors. It is concluded that these beta-glucanases differ in such a way that I preferentially continues to degrade fragments produced by endo-hydrolytic attack on long chains ('multiple attack' action pattern), while II hydrolyses internal linkages of the longest chains available ('multi-chain attack').