Structures of Multi-Branched Dextrins Produced by Saccharifying «-Amylase from Starch

From the digest of /3-limit dextrin (prepared from glutinous rice starch) with sac-charifying a-amylase of Bacillus subtilis [EC 3.2.1.1] (BSA), two extensively branched dextrins consisting of nine (No. 6,1 Fig. 1) and ten (No. 7, Fig. 1) glucose units were isolated by paper chromatography. Structural analysis using various enzymes revealed that No. 6 and No. 7 were both mixtures of four triply branched dextrins. They had structures which were built up with 63-a-glucosylmaltotriose and/or 62-a-glucosylmaltose as a linking unit. However, the branching configuration and the minimum a-l, 4-glucosidic linkages existing between two branches followed one of the three structures shown below: 1) O—O, 2) O—O —O, and 3) O—O —O —.2 In a previous paper (7) it was reported that all the doubly branched dextrins produced as a limit dextrin by saccharifying a-amylase [EC 3.2.1.1] of Bacillus subtilis (BSA) ( 2- 4) con-tained a 63-a-glucosylmaltotriose moiety at the reducing end and an isomaltosyl moiety at the non-reducing end. The branched dextrins were thus regarded as condensation products of 63-a-glucosylmaltotriose or of 62-a-glucosylmaltose and the former dextrin. Kainuma and French (5) have suggested that a branching configura-tion similar to that of our doubly branched dextrins is present in starch. 1 A small quantity of branched decaose was con-tained and its structure was also determined. 2 O, glucose residue; | , a-l,6-glucosidic linkage; —, a-l, 4-glucosidic linkage. The purpose of the present work was to isolate and investigate the structures of more extensively branched dextrins which are pro-duced by saccharifying a-amylase as a limit dextrin. In the present paper, implication of the results is also discussed to deduce some general rules for branching configuration of glutinous rice starch amylopectin