Three kinds of novel cyclic isomaltooligosaccharides were isolated from the culture broth of a strain of Bacillus sp. T -3040, which had been isolated from soil. They were identified as cycloisomalto-heptaose, -octaose, and -nonaose, respectively, on the basis of their mass spectra, proton nuclear magnetic resonance spectra, carbon nuclear magnetic resonance spectra, infrared spectra, reducing power, and results of enzymatic analysis using endo-dextranase and exo-dextranase. They also showed features similar to cyclodextrins upon high-pressure liquid chromatography analysis using an ODS column.Cyclodextrins (CDs; a-, f3-, and y-cyclodextrin) are cyclic glucose oligomers that consist of six, seven, and eight D-glucoses bound by a-l,4 linkages, respectively.1) Since CDs have hydrophobic cavities in the center of their rings, they can form inclusion complexes with hydrophobic substances.2 ) Many studies, especially those aimed at application for foods and madicines, have been done using this feature. 3,4) Apart from CDs, several other cyclic oligo saccharides are known, for example cyclic f3-1,2 glucans (cyclosophoraoses),5) cyclic f3-1,3 glucan (f3-1,3-linked cyclogluco-hexaose),6) cyclic f3-2,1 fructans (cycloinulooligo saccharides; CFs),7) cyclorhamno-hexaose (a-cycloawaodorin),8) and cyclomanno-hexaose. 9 ) Cyclosophoraoses are synthesized by some species of Rhizobium and Agrobacterium through the action of cyclic f3-1,2 glucan synthetase.10 ) CFs are synthesized from inulin by Bacillus circulans through the action of cycloinulo-oligosaccharide fructanotransferase (CFTase).ll) Other oligo saccharides have been synthesized by chemical methods. These results led us to consider that novel cyclic oligo saccharides, synthesized from other polysaccharides, might exist. We therefore attempted to screen for cyclic isomaltooligosaccharides consisting ofD-glucose bound by a-I ,6 linkages, which have never been reported previously.We have isolated from soil one strain of bacteria that produced non-reducing sugars from dextran (a-l,6 glucan). From several analytical experiments, it was confirmed that these sugars were novel cyclic oligosaccharides, cycloisomaltooligosaccharides. This paper describes the purification and characterization of cyclic isomaltooligosaccharides.
Materials and MethodsMaterials. Blue dextran 2000 and Dextran T2000 were purchased from Pharmacia. A series of isomaltooligosaccharides used as standards, from isomaltose to isomaltoheptaose, were purchased from Seikagaku Co., Japan, and those from isomaltooctaose to isomaltodecaose were obtained from Funakoshi Co., Japan. Bactotryptone and yeast extract were purchased from Difco and peptone was purchased from Kyokuto Seiyaku Kougyo Co., Japan.Enzymes. Endo-dextranase (l,6-IX-D-glucan-6-glucanohydrolase; EC 3.2.1.11) from Penicillium sp. and glucodextranase (1,6-IX-D-glucan glucohydrolase; EC 3.2.1.70) from Arthrobacter globiformis 142 were purchased from the Sigma Chemical Co. and Seikagaku Co., Japan, respectively.Cultures. Strain T-3040 used for the t...