A preliminary characterization of digestive proteases in the posterior midgut of the stable fly Stomoxys calcitrans (L.) (Diptera:Muscidae)

Abstract Proteinases contained in the posterior midgut of the stable fly, Stomoxys calcitrans (L.), have been tentatively identified by posterior midgut hydrolysis of synthetic substrates. Trypsin was identified by maximal hydrolysis of benzoyl- dl -arginine -p- nitroanilide (BAPNA) and tosyl- l -arginine methyl ester (TAME) at pH 8.0 and chymotrypsin, by maximal hydrolysis of benzoyl- l -tyrosine ethyl ester (BTEE) at pH 8.0. Carboxypeptidase A and B were identified by their maximal hydrolysis of hippuryl- dl -phenyllactic acid and hippuryl- l -arginine at pH 8.0 and 7.5 respectively and aminopeptidase was identified by maximal hydrolysis of leucine- p -nitroanilide at pH 7.5. Molecular weights, determined using gel exclusion chromatography, for proteinases were 19,500 for trypsin, 27,500 and 64,000 for chymotrypsin. Hydrolytic activity for the protein substrate haemoglobin occurred as two peaks with molecular weights of 19,500 and 27,500. Molecular weights for the peptidases were; carboxypeptidase A 26,000, carboxypeptidase B , 28,500 and greater than 1,500,000 for aminopeptidase. These results indicate that the posterior midgut of the stable fly contains both proteinases and peptidases necessary for proteolytic breakdown of the ingested blood meal.