An enzymatically produced novel cyclomaltopentaose cyclized from amylose by an α-(1→6)-linkage, cyclo-{→6)-α-d-Glcp-(1→4)-α-d-Glcp-(1→4)-α-d-Glcp-(1→4)-α-d-Glcp-(1→4)-α-d-Glcp-(1→}

Abstract A bacterial strain AM7, isolated from soil and identified as Bacillus circulans , produced two kinds of novel cyclic oligosaccharides. The cyclic oligosaccharides were produced from amylose using a culture supernatant of the strain as the enzyme preparation. The major product was a cyclomaltopentaose cyclized by an α-(1→6)-linkage, cyclo -{→6)-α- d -Glc p -(1→4)-α- d -Glc p -(1→4)-α- d -Glc p -(1→4)-α- d -Glc p -(1→4)-α- d -Glc p -(1→}. The other minor product was cyclomaltohexaose cyclized by an α-(1→6)-linkage, cyclo -{→6)-α- d -Glc p -(1→4)-α- d -Glc p -(1→4)-α- d -Glc p -(1→4)-α- d -Glc p -(1→4)-α- d -Glc p -(1→4)-α- d -Glc p -(1→}. We propose the names isocyclomaltopentaose (ICG5) and isocyclomaltohexaose (ICG6) for these novel cyclic maltooligosaccharides having one α-(1→6)-linkage. ICG5 was digested by α-amylase derived from Aspergillus oryzae , cyclomaltodextrin glucanotransferase (CGTase) from Bacillus stearothermophilus , and maltogenic α-amylase. On the other hand, ICG6 was digested by CGTase from B. stearothermophilus and B. circulans , and maltogenic α-amylase. This is the first report of enzymatically produced cyclomaltopentaose and cyclomaltohexaose, which have an α-(1→6)-linkage in their molecules.