Cyclodextrin glycosyltransferase from Bacillus circulans DF 9R: Activity and kinetic studies

Activity characteristics and kinetic aspects of a cyclodextrin glycosyltransferase (CGTase) from Bacillus circulans DF 9R were studied. A mixture of α-, β- and γ-cyclodextrins (CDs), glucose, maltose and negligible amounts of longer linear dextrins were produced from gelatinized amylose, amylopectin and starch from different sources. In the coupling reaction, CDs were the substrates in the presence of acceptors such as maltose and/or longer oligosaccharides. From oligosaccharides formed by three or more glucose units, this enzyme produced linear chains of several lengths which were then cyclized. CGTase catalytic efficiency was compared employing an analytical grade starch and cassava starch for food use. Since the results obtained were similar for both starches, the use of an economic starch is an advantage. CGTase was inhibited by the substrate and its own products. Starch concentrations over 20 mg/mL inhibited the cyclizing activity. CDs behaved as competitive inhibitors and maltose as an uncompetitive inhibitor while maltotriose showed a mixed inhibition pattern. Limit dextrins showed a scarce inhibitory effect on enzyme activity. CD production could be improved with an ultrafiltration membrane reactor for continuous removal of the products; the starch concentration should be maintained below an inhibitory concentration and limit dextrins would remain in the reactor without affecting enzyme activity.