Delta endotoxin inhibits a phosphatase in midgut epithelial membranes of Heliothis virescens

Abstract

A vanadate- and delta endotoxin-sensitive phosphatase copurified with plasma membranes and brush border membranes from the midgut epithelium of Heliothis virescens. Phosphatase activity was stimulated under alkaline conditions. Total phosphatase activity was inhibited 60% in the midgut membranes by 360 nM delta endotoxin with a K i = 76 nM. Brush border membranes were inhibited 75% by 1.47 μM delta endotoxin with a K i = 64.7 nM. Vanadate (200 μM) completely inhibited the toxinsensitive alkaline phosphatase. A 72 kDa protein was phosphorylated when membranes were incubated with Mg 2+ and [ 32P]orthophosphate, and phosphorylation was inhibited by both vanadate and delta endotoxin, suggesting that destabilization of this phosphoprotein was responsible for phosphatase inhibition.