Castanospermine: an apparent tight-binding inhibitor of hepatic lysosomal alpha-glucosidase

Castanospermine is a potent inhibitor of rat hepatic lysosomal alpha-glucosidase in vitro. The alkaloid showed time-dependent inhibition with an IC50 of 5 X 10(-6) M without preincubation and 1 X 10(-7) M with 1 hr of preincubation. Inhibition appeared competitive without preincubation but noncompetitive after preincubation. The time-dependent inactivation of the enzyme followed pseudo-first-order kinetics with an inactivation constant of 1.2 X 10(3) M-1 sec-1. The apparent irreversibility of enzyme inhibition by castanospermine is postulated to be by tight-binding inhibition.