BLOOD DIGESTION IN THE MOSQUITO, ANOPHELES-STEPHENSI LISTON (DIPTERA, CULICIDAE) - PARTIAL CHARACTERIZATION AND POST-FEEDING ACTIVITY OF MIDGUT AMINOPEPTIDASES

Aminopeptidase activity was partially characterized from midguts of Anopheles stephensi Liston which had been dissected 30 h after blood feeding. In crude midgut homogenate supernatants the aminopeptidases showed optimum activity at pH 8.0 and preferentially hydrolyzed alanine‐ and leucine‐terminal amino acid substrates. Methionine, proline, lysine, and arginine terminal substrates were hydrolysed, but not glutamic acid. Activity was stimulated by Mg2+, EDTA, and low Ca2+ concentrations, while Mn2+, Tris, 1,10 phenanthroline, and higher Ca2+ concentrations were inhibitory. Supernatants from midguts homogenized in 1% Triton X‐100 showed a twofold increase in activity. Differential centrifugation of midgut homogenates demonstrated 45% of the total activity in a putative microvillar pellet and 32% in a soluble fraction. More than 92% of the total activity was solubilized after homogenization in Triton X‐100. Activity in homogenate supernatants was restricted to one major peak (Mr = 552,000) with a higher molecular weight shoulder. Three distinct peaks of aminopeptidase activity were observed forllowing Triton X‐100 treatment: a minor high molecular weight peak (Mr = 552,000), and two major peaks at Mr = 123,000 and Mr = 32,000 respectively. The activity of aminopeptidase increased after a blood meal, in parallel to the post‐feeding changes in trypsin activity, indicating its important role in secondary digestion of blood meal proteins. Copyright © 1990 Wiley‐Liss, Inc.