Abstract
Results of this study suggest that two exoproteinases, lysosomal carboxypeptidase B and aminopeptidase, are present in the posterior midgut of Rhodnius prolixus Stål. Digestive midgut lysosomal carboxypeptidase B hydrolysed hippuryl- dl-phenyllactic acid (HPLA) and N- carbobenzoxy- l-glutamyl- l-tyrosine with maximal activities at pH 4.0 and 3.9 respectively. Activity was higher in the presence of thiol compounds (cysteine, glutathione, dithiothreitol and mercaptoethanol) and was inhibited by iodoacetamide (IAA) and tosyl- l-lysine chloromethyl ketone (TLCK). Digestive midgut aminopeptidase hydrolysed leucine- p-nitroanilide (LPNA) with maximal activity at pH 8.0. Magnesium activated LPNA hydrolysis whereas calcium, thiol compounds and EDTA inhibited activity. IAA and TLCK had no effect. Aminopeptidase was located in the gut wall and lysosomal carboxypeptidase B was located in the gut lumen. The presence of lysosomal carboxypeptidase B and the previously described cathepsin B-like proteinase demonstrate that the digestive proteinases in R. prolixus are unique among those described for blood feeding insects.
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