Enzymatic properties and the primary structure of a β-1,3-glucanase from the digestive fluid of the Pacific abalone Haliotis discus hannai

摘要

A β-1,3-glucanase (EC 3.2.1.6) with a molecular mass of 33 kDa was isolated from the digestive fluid of the Pacific abalone Haliotis discus hannai by ammonium sulfate fractionation followed by conventional column chromatography. This enzyme, named HdLam33 in the present study, degraded laminarin and laminarioligosaccharides to laminaribiose and glucose with the optimal temperature and pH at 50℃ and 6.0, respectively. HdLam33 possessed transglycosylation activity, a characteristic property of glucan hydrolases that split glycoside linkage with a retaining manner. By the transglycosylation reaction of HdLam33, the laminaribiose unit in the non-reducing terminus of laminaritriose (donor substrate) was transferred to a free laminaribiose (acceptor substrate) resulting laminaritetraose and glucose. The resulted laminaritetraose was subsequently hydrolyzed by HdLam33 into two moles of glucose and one mole of laminaribiose. The primary structure of HdLam33 was analyzed by the cDNA method. The deduced amino-acid sequence of 329 residues corresponding to the catalytic domain of HdLam33 showed 56-61% amino-acid identity with those of other molluscan β-1,3-glucanases which have been identified as glycoside hydrolase family 16 enzymes.