Catalytic properties and mode of action of endo-(1 -> 3)-beta-D-glucanase and beta-D-glucosidase from the marine mollusk Littorina kurila

摘要

A complex of the enzymes from the liver of the marine mollusk Littorina kurila that hydrolyzes laminaran was investigated. Two (1-->3)-beta-D-glucanases (G-I and G-II) were isolated. The molecular mass of G-I as estimated by gel-permeation chromatography and SIDS-PAGE analysis was 32 and 40 kDa, respectively. The G-II molecular mass according to SIDS-PAGE analysis was about 200 kDa. The pH optimum for both G-I and G-II was pH 5.4. The G-I had narrow substrate specificity and hydrolyzed only the (1-->3)-beta-D-glucosidic bonds in the mixed (1-->3),(1-->6)- and (1-->3),(1-->4)-beta-D-glucans down to glucose and glucooligosaccharides. This enzyme acted with retention of the anomeric configuration and catalyzed a transglycosylation reaction. G-I was classified as the glucan endo-(1-->3)-beta-D-glucosidase (EC 3.2.1.39). G-II exhibited both exo-glucanase and beta-D-glucoside activities. This enzyme released from the laminaran glucose as a single product, but retained the anomeric center configuration and possessed transglycosylation activity. The hydrolysis rate of glucooligosaccharides by G-I decreased with an increase of the substrate's degree of polymerization. In addition to (1-->3)-beta-D-glucanase activity, the enzyme had the ability to hydrolyze p-nitrophenyl beta-D-glucoside and beta-D-glucobioses: laminaribiose, gentiobiose, and cellobiose, with the rate ratio of 50:12: 1. G-II may correspond to P-D-glucoside glucohydrolase (EC 3.2.1.21). (C) 2008 Elsevier Ltd. All rights reserved.