Trehazolin, a slow, tight-binding inhibitor of silkworm trehalase

Abstract Mechanisms of enzyme inhibition by trehazolin, a new inhibitor of trehalase (Ando et al. (1991) J. Antibiot. 44, 1165), were investigated using purified soluble silkworm trehalase and other glycosidases. Trehazolin inhibited trehalase with an IC 50 value of 27 nM, whereas some other exo-α-glucosidases were inhibited only weakly, with IC 50 values ranging from 7 to 370 μM. Other glycosidases tested were not inhibited by 500 μM trehazolin. The inhibition of trehalase by trehazolin was competitive with respect to trehalose. A notable feature of the inhibition was a slow progression of the association and dissociation of the enzyme-inhibitor complex. Preincubation of the enzyme and the inhibitor at 37°C potentiated the inhibition by 10-times in a time-dependent manner up to 6 h. Dialysis of the inactivated enzyme recovered the enzymatic activity very slowly, and the rate constant for the dissociation at 37°C was 7.3 · 10 −2 h −1 . Trehalamine, a deglucosylated form of trehazolin, inhibited both silkworm trehalase and exo-α-glucosidases only weakly. The inhibition of trehalase by trehalamine was reversible. Rat isomaltase inhibition by trehazolin and sucrase inhibition by trehalamine were also reversible. Taken together, trehazolin is a specific slow, tight-binding inhibitor of trehalase, and the glucose moiety of the inhibitor is essential to the tight binding.