Transglycosylation Reaction and Acceptor Specificity of Exo- and Endo-type Cellulases

Abstract

The possibility of transglycosylation and acceptor specificity of cellulases, CBH I, CBH II, EG II (Trichoderma reesei), Ex-1 (Irpex lacteus) and Exo-A (Aspergillus niger) was investigated by using cellotriose (G3) and p-nitrophenyl-β-D-glucoside (pNPG1) as a donor and an acceptor, respectively. Among exo-type cellulases, CBH I effectively accumulated two transfer products, pNP-β-D-cellotrioside and 3-O-β-D-cellobiosyl-pNP-β-D-glucoside. They were produced by the transfer of a cellobiosyl unit resulting in G3 hydrolysis to pNPG1 with β-1,4 or β-1,3 glycosidic bonds, respectively. On the other hand, endo-type cellulase EG II, produced pNP-β-D-cellobioside, pNP-β-D-gentiobioside and pNP-β-D-laminaribioside. These might be synthesized by the glucosyl transfer produced from G3 or pNPG1 to pNPG1 with β-1,4, β-1,6 or β-1,3 glycosidic bonds. Furthermore, CBH I and EG II catalyzed transglycosylation to various pNP-glycosides. From the study of acceptor specificity for CBH I and EG II, pNP-α-D-galactoside in addition to pNP-glycosides with β-configuration was used as the acceptor.