Inhibition of an insect midgut trehalase by dioxane and δ-gluconolactone: Enzyme pK a values and geometric relationships at the active site

Abstract

1. 1. Inhibition of the Rhynchosciara americana midgut trehalase (α, α'-trehalose glucohydrolase, EC 3.2.1.28) by the competitive inhibitor dioxane have been studied. 2. 2. Determinations of the K i of dioxane at different pH provided the true pK a values of the prototropic groups of the trehalase active site (pK a 5.2 and 8.2), which are in agreement with those determined previously from kinetic and chemical modification data. 3. 3. Dioxane only changes the enzyme pK a values if bound at the enzyme active site. 4. 4. Gluconic acid does not inhibit the trehalase, in contrast to δ-gluconolactone which is a simple intersecting linear inhibitor. 5. 5. Multiple inhibition analyses showed that δ-gluconolactone and Tris bind at the same site in the trehalase active center, whereas dioxane binds closer to δ-gluconolactone than to Tris. 6. 6. The data support the assumption that dioxane binds at the middle portion of the trehalase active site.