Cyclomaltaoses (cyclodextrins, cycloamyloses) have been widely studied because of their unique structures and properties'. However, there have been only limited studies of branched cyclomaltaoses since they were discovered by French et aL2. These cyclomaltaose derivatives have a D-glucose or a (l-+4)-a-D-glucan branch attached to the main cyclic structure by an a-(1+6) linkage. Taylor and Whelan3y4 reported that 6-cY-o-glucosylcyclomaltohexaose and 6-Cu-D-glucosylcyclomaltoheptaose (GcG,) are suitable substrates for determining the activity of amylo-1,6-glucosidase (EC 3.2.1.33). They obtained a mixture of these glucosylcyclomaltaoses from the glucoamylase-treated mother liquor of a large-scale preparation of the non-branched cyclomaltaoses from starch by p.c., or separated them by Sephadex G-15 chromatography followed by p.c. Kobayashi et al. prepared" the branched cyclomaltaoses by fractionation with organic solvents followed by p.c., and reported some propertie@. In these studies, however, the purity and the structure of the product were not reported in detail. We have isolated pure GcG7 from a commercial starch syrup (Celdex) and analysed its structure in detail.
Gel-permeation chromatography was the main technique used for the isolation. The commercial starting-material, Celdex, is a concentrated mother liquor remaining after the separation of crystalline cyclomaltoheptaose (cG,), and contains D-glucose, oligosaccharides, non-cyclic dextrins, and cyclomaltaoses in addition to branched cyclomaltaoses. This mixture was treated twice with crude glucoamylase to hydrolyse the non-cyclic dextrins and oligosaccharides and to shorten the branches of the branched cyclomaltaoses.
After removing the D-glucose with baker's yeast, the remaining material was subjected to chromatography on Sephadex G-15 (Fig. l), and the fractions (50-68) that produced glycerol on Smith degradation and had almost no reducing power were combined. Most of the noncyclic dextrins and cG, were removed by using this column. Cyclomaltohexaose (cGg) was then separated from the branched cyclomaltaoses by chromatography on *To whom correspondence should be sent.