Carboxypeptidase B in Anopheles gambiae (Diptera: Culicidae): effects of abdominal distention and blood ingestion.

Carboxypeptidase B (CPB) activity was detected in the guts of strain G-3 of Anopheles gambiae (Giles) and Aedes aegypti (L.). Mosquitoes were examined 3-5 d after emergence following exposure to 20% sucrose, from 0 to 4 h after feeding on a meal of latex beads in saline, and from 0 to 96 h after blood feeding. CPB activity was assayed in whole-gut homogenates, including lumenal contents and peritrophic matrix, by following the hydrolysis of a substrate specific for CPB-[3H]-benzoyl-L-Phe-L-Arg. Homogenates were divided into cytosolic plus lumenal components and membrane-associated components. Activity levels changed in response to feeding, decreasing in response to distention by saline plus latex and increasing only in response to blood. Overall, CPB activity was higher in unfed An. gambiae than in unfed Ae. aegypti. Detection of CPB activity in the peritrophic matrix of both species indicated that this enzyme was secreted actively into the gut lumen. In An. gambiae, CPB activity was optimal at pH 8, and thiol-type CPB was the predominant form detected. The data indicated that CPB in An. gambiae was regulated by both physical and chemical factors.