Specificity of action of an insect proteinase purified from wheat grain infested by the New Zealand wheat bug, Nysius huttoni

A salivary proteinase from the New Zealand wheat bug (Nysius huttoni) was partially purified and analysed for substrate specificity by a variety of techniques on the following proteins: wheat, rye, barley and corn proteins, haemoglobin, bovine serum albumin, cytochrome c, cytochrome c oxidase, elastin, collagen, gelatine, keratin (hide powder), fibrin, azo-casein, α-casein, β-casein and κ-casein. The only proteins substantially hydrolysed (> 50%) by Nysius-proteinase were the high Mr glutenin subunits of wheat, the high Mr secalin and Mr 60,000 γ-secalin of rye, the d-hordeins of barley, the Mr 70,000, Mr 66,000 and Mr 58,000 C hordeins, and β-casein subunit of bovine milk. Sequence analysis of the peptide products of enzyme reaction on high Mr glutenin subunits, β-casein and κ-casein revealed that glutamine occupied the P1 position relative to the scissile bond at all cleavage sites. Proline in the P3 or P4 position, and particular residues in the P′1 position relative to the scissile bond may also be preferred structural features. A variety of fluorogenic substrates made from synthetic peptides with glutamine in the P1 position relative to the fluorogenic group were tested with the enzyme, but none reacted.