Sugar digestion in mosquitoes: identification and characterization of three midgut alpha-glucosidases of the neo-tropical malaria vector Anopheles aquasalis (Diptera: Culicidae).

Dietary carbohydrates provide an important source of energy for flight, and contribute to longevity and fecundity of mosquitoes. The most common sugar mosquitoes ingest is sucrose, and digestion of this substance is carried out mainly by alpha-glucosidases. In the current work, we tested the efficiency of sucrose on Anopheles aquasalis female diet. The best longevity (days) was reached when sugar was available in the diet, whereas most only blood fed females were dead 6 days after emergence. Three alpha-glucosidase isoforms were detected in the adult female midgut, named alphaGlu1, alphaGlu2 and alphaGlu3. These are acidic alpha-glucosidases with optima pH around pH 5.5. alphaGlu1 and alphaGlu2 are present in both secreted and membrane-bound forms, whereas alpha-Glu3 only in anchored to membranes. The alpha-glucosidase activity is concentrated mainly in the posterior midgut (70%), both in non-fed or 10% sucrose fed females. The single form of these alpha-glucosidases seemed to be approximately 70 kDa polypeptides, although alphaGlu2 is presented in >or=600 kDa self-aggregates. Km values of alphaGlu1, alphaGlu2 and alphaGlu3 differed significantly from each other, supporting the statement that three alpha-glucosidases are produced in the female midgut. Together, all data suggest that sugar is an essential component of A. aquasalis female diet. In addition, alpha-glucosidases are synthesized in the same place where sucrose is digested and absorbed, the midgut.