Vertebrate serum inhibitors of Aedes aegypti trypsin

A trypsin from the midgut of Aedes aegypti was partially purified. Its molecular weight was estimated as 21,500. This enzyme hydrolysed α-N-benzoyl-L-arginine ethyl ester (BAEE) and 2-N-benzoyl-DL-arginine-p-nitroanilide HCl (BAPNA). For the trypsin esterolytic activity the pH optimum was 7.9 and Michaelis-Menten constants were 0.47 mM for BAPNA and 2.24 mM for denatured bovine haemoglobin. The trypsin esterolytic activity was inhibited by the sera of 17 vertebrate species and by the haemolymph of Periplaneta americana. The inhibition capacity was relatively high in birds and low in an elasmobranch, with mammals, a reptile, a frog, teleosts, and an insect in the middle range. The number of inhibitors and their approximate molecular weights in each serum was studied by Sephadex gel chromatography.