Cyclization reaction catalyzed by glycogen debranching enzyme (EC 2.4.1.25/EC 3.2.1.33) and its potential for cycloamylose production

Glycogen debranching enzyme (GDE) has 4-a-glucanotransferase and amylo-1,6-glucosidase activities in the single polypeptide chain. We analyzed the detailed action profile of GDE from <i>Saccharomyces cerevisiae</i> on amylose and tested whether GDE catalyzes cyclization of amylose. GDE treatment resulted in a rapid reduction of absorbance of iodine-amylose complex and the accumulation of a product that was resistant to an exoamylase (glucoamylase [GA]) but was degraded by an endo-type a-amylase to glucose and maltose. These results indicated that GDE catalyzed cyclization of amylose to produce cyclic a-1,4 glucan (cycloamylose). The formation of cycloamylose was confirmed by high-performance anion-exchange chromatography, and the size was shown to range from a degree of polymerization of 11 to a degree of polymerization around 50. The minimum size and the size distribution of cycloamylose were different from those of cycloamylose produced by other 4-a-glucanotransferases. GDE also efficiently produced cycloamylose even from the branched glucan substrate, starch, demonstrating its potential for industrial production of cycloamylose.