Catalytic properties and mode of action of endo-(1→3)-β-d-glucanase and β-d-glucosidase from the marine mollusk Littorina kurila

A complex of the enzymes from the liver of the marine mollusk Littorina kurila that hydrolyzes laminaran was investigated. Two (1→3)-β-d-glucanases (G-I and G-II) were isolated. The molecular mass of G-I as estimated by gel-permeation chromatography and SDS–PAGE analysis was 32 and 40 kDa, respectively. The G-II molecular mass according to SDS–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)-β-d-glucosidic bonds in the mixed (1→3),(1→6)- and (1→3),(1→4)-β-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)-β-d-glucosidase (EC 3.2.1.39).G-II exhibited both exo-glucanase and β-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)-β-d-glucanase activity, the enzyme had the ability to hydrolyze p-nitrophenyl β-d-glucoside and β-d-glucobioses: laminaribiose, gentiobiose, and cellobiose, with the rate ratio of 50:12:1. G-II may correspond to β-d-glucoside glucohydrolase (EC 3.2.1.21).

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