Endoproteinase activity in the posterior midgut of Rhodnius prolixus Stål (Hemiptera: Reduviidae)

Abstract

Tests with homogenates of digestive midgut of Rhodnius prolixus Stål showed that hydrolysis of N- benzoyl- dl- arginine naphthylamine (BANA), N- benzoyl- dl- arginine-p- nitroanilide (BAPNA) and casein was activated by EDTA and thiol reagents (cysteine, glutathione, mercaptoethanol, and dithiothreitol) but the hydrolysis of N- benzoyl- l-tyrosine ethyl ester (BTEE) was inhibited. Iodoacetamide and tosyl- l-lysine chloromethyl ketone inhibited BAPNA and casein hydrolysis but did not affect BTEE hydrolysis. Iodoacetamide also inhibited BANA hydrolysis. Horse serum inhibited hydrolysis of all tested substrates but soybean trypsin inhibitor inhibited only casein and BTEE activities. Metal ions Ca 2+, Mg 2+ and Mn 2+ had no affect on hydrolysis of BTEE, BANA or casein when crude midgut homogenate was used. These results suggest that at least two proteinases (one, cathepsin B-like, and another which is a thiol- and EDTA-sensitive endoproteinase) are present in the posterior midgut of R. prolixus.