Kinetics and inhibition of cyclomaltodextrinase from alkalophilic Bacillussp I-5

The cyclomaltodextrinase from alkalophilic Bacillus sp, I-5 (CDase I-5) was expressed in Escherichia coli and the purified enzyme was used for charact erization of the enzyme action. The hydrolysis products were monitored by b oth HPLC and high-performance ion chromatography analysis that enable the k inetic analysis of the cyclomaltodextrin (CD)-degrading reaction. Analysis of the kinetics of cyclomaltodextrin hydrolysis by CDase I-5 indicated that ring-opening of the cyclomaltodextrin was the major limiting step and that CDase I-5 preferentially degraded the linear maltodextrin chain by removin g the maltose unit. The substrate binding affinity of the enzyme was almost same for those of cyclomaltodextrins while the rate of ring-opening was th e fastest for cyclomaltoheptaose. Acarbose and methyl 6-amino-6-deoxy-alpha -D-glucopyranoside were relatively strong competitive inhibitors with K-i v alues of 1.24 x 10(-3) and 8.44 x 10(-1) mM, respectively. Both inhibitors are likely to inhibit the ring-opening step of the CD degradation reaction. (C) 2000 Academic Press.