Substrate specificities of exo- and endo-type cellulases in the hydrolysis of beta-(1----3)- and beta-(1----4)-mixed D-glucans.
An exo-type cellulase (Ex-1) was extracted from Irpex lacteus (Polyporus tulipiferae) and purified essentially to homogeneity. This cellulase attacked cellulosic substrates in an exo-wise fashion to produce almost exclusively cellobiose. In contrast, Ex-1 was found to attack beta-glucans having beta-(1----3)- and beta-(1----4)-mixed linkages in a way similar to an endo-type cellulase. The products formed from barley glucan by Ex-1 were 3(2)-O-beta-D-cellobiosyl-cellobiose much greater than 3(2)-O-beta-D-glucosyl-cellobiose greater than cellobiose much greater than or equal to cellotriose much greater than glucose in the early stage, but no laminaribiose was produced. An endo-type cellulase (En-1) obtained from the same fungus also hydrolyzed beta-glucans but in a typical endo-wise fashion and the products from barley glucan were 3(2)-O-beta-D-glucosyl-cellobiose much greater than 3(2)-O-beta-D-cellobiosyl-cellobiose greater than cellobiose much greater than laminaribiose; no glucose or cellotriose was produced. Thus, it seems likely that En-1 can attack any intramolecular linkage of beta-glucan, while Ex-1 requires the presence of at least cellobiosyl residues adjacent to a beta-(1----3)-D-linked glucosyl residue. This finding, together with the mode of hydrolysis of cellulosic substrates by Ex-1, suggests that the stereochemical structure of successive beta-(1----4)-cellobiosyl residues inserted by beta-(1----3)-D-glucosidic linkage is permissible in the action of Ex-1, although this enzyme prefers the beta-(1----4)-linked cellobiosyl sequence.
Kanda
T
T
Department of Industrial Chemistry, Faculty of Engineering, Shinshu University, Nagano.
Yatomi
H
H
Makishima
S
S
Amano
Y
Y
Nisizawa
K
K
D002480:Cellulase / Q000378:metabolism*; D043366:Cellulose 1,4-beta-Cellobiosidase; D002855:Chromatography, Thin Layer; D004591:Electrophoresis, Polyacrylamide Gel; D005936:Glucans / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D011124:Polyporaceae / Q000201:enzymology; D013379:Substrate Specificity; D013997:Time Factors; D047071:beta-Glucans
D005936:Glucans; D047071:beta-Glucans; C040088:1,4-glucan; C033363:beta-1,3-glucan; D006026:Glycoside Hydrolases; D002480:Cellulase; D043366:Cellulose 1,4-beta-Cellobiosidase