Dormant Activity of Cyclodextrin Glucanotransferase on Dextran Afforded the Molecular Changes

Abstract

The action of cyclodextrin glucanotransferase (CGTase) on clinical dextran was demonstrated under the reaction conditions of high concentrations of enzyme and substrate. CGTase showed noticeable affinity to Sephadex G-15 gel, and lower but definite hydrolysis reaction of dextran compared with soluble starch was kinetically evaluated. CGTase seemed to cause the molecular disproportionation of dextran, which was suggested by the product analysis after ethanol fractionation of the reaction mixture. The action of the CGTase on dextran reached a maximum at higher pH of 9.5 and temperature of 50°C than with soluble starch as a substrate. Moreover, the addition of surfactant, SDS, or acceptor molecule, such as methyl α-glucoside, greatly affected the CGTase reaction. Changes in molecular weight of the dextran indicated that a clear difference in molecular weight distribution of CGTase-treated dextran had occurred, although the increase in reducing sugar was very small. That is, compared with the dextran (Mw 63, 000), both lower (Mw 10, 000) and higher (more than Mw 500, 000) molecular weight products were obtained. These results strongly suggested evidence for the action of CGTase on α-1, 6-linked dextran.