Preliminary characterisation of digestive proteases of the green mirid, Creontiades dilutus (Hemiptera: Miridae)

Protease activities in the secreted saliva, salivary glands and midgut of the green mirid, Creontiades dilutus, were investigated. The saliva and salivary glands had more protease activity than the midgut, but no differences in protease activity levels were detected between male and female mirids, adult mirids and third instar nymphs, or between fed and starved mirids. In the salivary glands, chymotrypsin-like serine proteases predominated, as characterised by inhibitor specificity, basic pH optima, and hydrolysis of N-benzoyl-L-tyrosine p-nitroanilide and N-succinyl-ala-ala-pro-leu p-nitroanilide. The pH optimum of midgut extracts was acidic (pH 4), implying that acidic proteases predominate. However, protease activity was inhibited substantially by both aprotinin and E-64, suggesting the presence of both serine and cysteine proteases in the midgut of the green mirid.