Purification and Characterization of Highly Branched α-Glucan-Producing Enzymes from Paenibacillus sp PP710

Highly branched alpha-glucan molecules exhibit low digestibility for alpha-amylase and glucoamylase, and abundant in alpha-(1 -> 3)-, alpha-(1 ->-6)-glucosidic linkages and alpha-(1 -> 6)-linked branch points where another glucosyl chain is initiated through art alpha-(1 -> 3)-linkage. From a culture supernatant of Paenibacillus sp. PP710, we purified alpha-glucosidase (AGL) and alpha-amylase (AMY), which were involved in the production of highly branched alpha-glucan from maltodextrin. AGL catalyzed the transglucosylation reaction of a glucosyl residue to a nonreducing-end glucosyl residue by alpha-1,6-, alpha-1,4-, and alpha-1,3-linkages. AMY catalyzed the hydrolysis of the alpha-1,4-linkage and the intermolecular or intramolecular transfer of maltooligosaccharide like cyclodextrin glucanotransferase (CGTase). It. also catalyzed the transfer of an alpha-1,4-glucosyl chain to a C3- or C4-hydroxyl group in the alpha-1,4- or alpha-1,6-linked nonreducing-end residue or the alpha-1,6-linked residue located in the other chains. Hence AMY was regarded as a novel enzyme. We think that the mechanism of formation of highly branched alpha-glucan from maltodextrin is as follows: alpha-1,6- and alpha-1,3-linked residues are generated by the transglucosylation of AGL at the nonreducing ends of glucosyl chains. Then AMY catalyzes the transfer of alpha-1,4-chains to C3- or C4-hydroxyl groups in the alpha-1,4- or alpha-1,6-linked residues generated by AGL. Thus the concerted reactions of both AGL and AMY are necessary to produce the highly branched a-glucan from maltodextrin.