ABSTRACT
Highly branched α-glucan molecules exhibit low digestibility for α-amylase and glucoamylase, and abundant in α-(1â3)-, α-(1â6)-glucosidic linkages and α-(1â6)-linked branch points where another glucosyl chain is initiated through an α-(1â3)-linkage. From a culture supernatant of Paenibacillus sp. PP710, we purified α-glucosidase (AGL) and α-amylase (AMY), which were involved in the production of highly branched α-glucan from maltodextrin. AGL catalyzed the transglucosylation reaction of a glucosyl residue to a nonreducing-end glucosyl residue by α-1,6-, α-1,4-, and α-1,3-linkages. AMY catalyzed the hydrolysis of the α-1,4-linkage and the intermolecular or intramolecular transfer of maltooligosaccharide like cyclodextrin glucanotransferase (CGTase). It also catalyzed the transfer of an α-1,4-glucosyl chain to a C3- or C4-hydroxyl group in the α-1,4- or α-1,6-linked nonreducing-end residue or the α-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 α-glucan from maltodextrin is as follows: α-1,6- and α-1,3-linked residues are generated by the transglucosylation of AGL at the nonreducing ends of glucosyl chains. Then AMY catalyzes the transfer of α-1,4-chains to C3- or C4-hydroxyl groups in the α-1,4- or α-1,6-linked residues generated by AGL. Thus the concerted reactions of both AGL and AMY are necessary to produce the highly branched α-glucan from maltodextrin.
Subject(s)
Glucans/biosynthesis , Oligosaccharides, Branched-Chain/biosynthesis , Paenibacillus/enzymology , Polysaccharides/metabolism , alpha-Amylases/isolation & purification , alpha-Glucosidases/isolation & purification , Biocatalysis , Carbohydrate Sequence , Chromatography, Gel , Chromatography, High Pressure Liquid , Electrophoresis, Polyacrylamide Gel , Glycosylation , Oligosaccharides/metabolism , Oxidation-Reduction , Paenibacillus/chemistry , alpha-Amylases/metabolism , alpha-Glucosidases/metabolismABSTRACT
The bacterial strain PP710, isolated from soil and identified as Paenibacillus species, produced a low-digestibility alpha-glucan containing a large amylase-resistant portion. This alpha-glucan was obtained in high yields from maltodextrin (dextrose equivalent 3) by using the condensed culture supernatant of the strain as the enzyme preparation. The water-soluble dietary fiber content of the low-digestibility alpha-glucan was 80.2%, and showed resistance to a rat intestinal enzyme preparation. The alpha-glucan was found to be a novel highly branched alpha-glucan by acid hydrolysis, NMR analysis, gel permeation chromatography, methylation analysis, and enzymatic digestion.
