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

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