TREHAZOLIN, A SLOW, TIGHT-BINDING INHIBITOR OF SILKWORM TREHALASE

Mechanisms of enzyme inhibition by trehazolin, a new inhibitor of treh alase (Ando et al. (1991) J. Antibiot. 44, 1165), were investigated us ing purified soluble silkworm trehalase and other glycosidases. Trehaz olin inhibited trehalase with an IC50 value of 27 nM, whereas some oth er exo-alpha-glucosidases were inhibited only weakly, with IC50 values ranging from 7 to 370 mu M. Other glycosidases tested were not inhibi ted by 500 mu M trehazolin. The inhibition of trehalase by trehazolin was competitive with respect to trehalose. A notable feature of the in hibition was a slow progression of the association and dissociation of the enzyme-inhibitor complex. Preincubation of the enzyme and the inh ibitor at 37 degrees C potentiated the inhibition by 10-times in a tim e-dependent manner up to 6 h. Dialysis of the inactivated enzyme recov ered the enzymatic activity very slowly, and the rate constant for the dissociation at 37 degrees C was 7.3 . 10(-2) h(-1). Trehalamine, a d eglucosylated form of trehazolin, inhibited both silkworm trehalase an d exo-alpha-glucosidases only weakly. The inhibition of trehalase by t rehalamine was reversible. Rat isomaltase inhibition by trehazolin and sucrase inhibition by trehalamine were also reversible. Taken togethe r, trehazolin is a specific slow, tight-binding inhibitor of trehalase , and the glucose moiety of the inhibitor is essential to the tight bi nding.