Cathepsin B and aminopeptidase in the posterior midgut of Phymata wolffii Stål (Hemiptera: Phymatidae)

The posterior midgut of the phymatid Phymata wolffii Stal contains cathepsin B and aminopeptidase activity. Identification of cathepsin B was based on maximal hydrolysis of benzoyl-DL-arginine-2-naphthylamide and benzoyl-DL-arginine-p-nitroanilide at pH 5.8 and 5.5, respectively. Cathepsin B hydrolysis of the tested substrates was activated by thiol chemicals and ethylenediaminetetraacetic acid (EDTA) and inhibited by tosyl-L-lysine chloromethyl ketone, iodoacetamide, and soybean trypsin inhibitor. Aminopeptidase hydrolyzed leucine-p-nitroanilide maximally at pH 7.8 and hydrolysis of the substrate was activated by magnesium and inhibited by EDTA, dithiothreitol, glutathione, and cysteine. The molecular weight of cathepsin B was 40 000 and was greater than 150 000 for aminopeptidase.