Inhibition of an insect midgut trehalase by dioxane and delta-gluconolactone: enzyme pKa values and geometric relationships at the active site.
1. Inhibition of the Rhynchosciara americana midgut trehalase (alpha, alpha'-trehalose glucohydrolase, EC 3.2.1.28) by the competitive inhibitor dioxane have been studied. 2. Determinations of the Ki of dioxane at different pH provided the true pKa values of the prototropic groups of the trehalase active site (pKa 5.2 and 8.2), which are in agreement with those determined previously from kinetic and chemical modification data. 3. Dioxane only changes the enzyme pKa values if bound at the enzyme active site. 4. Gluconic acid does not inhibit the trehalase, in contrast to delta-gluconolactone which is a simple intersecting linear inhibitor. 5. Multiple inhibition analyses showed that delta-gluconolactone and Tris bind at the same site in the trehalase active center, whereas dioxane binds closer to delta-gluconolactone than to Tris. 6. The data support the assumption that dioxane binds at the middle portion of the trehalase active site.
D000818:Animals; D001665:Binding Sites; D004064:Digestive System / Q000201:enzymology; D004146:Dioxanes / Q000494:pharmacology*; D004147:Dioxins / Q000494:pharmacology*; D004175:Diptera / Q000201:enzymology*; D005942:Gluconates / Q000494:pharmacology*; D007700:Kinetics; D007783:Lactones; D014198:Trehalase / Q000037:antagonists & inhibitors*
D004146:Dioxanes; D004147:Dioxins; D005942:Gluconates; D007783:Lactones; D014198:Trehalase; C025223:1,4-dioxane; C030691:gluconic acid; C010730:beta-glucono-1,5-lactone