Immunological control of scab mites: digestive enzymes as candidate compounds.

Phosphatases, C4 and C8 esterases, leucine and valine aminopeptidases, n-acetyl-beta-glucosaminidase, beta-glucosidase, beta-galactosidase and beta-glucuronidase were active in extracts of scab mites (Psoroptes spp.) raised on sheep or rabbits. Trypsin and chymotrypsin activities were not detected. Haemoglobin was hydrolysed by a detergent-soluble fraction of the mite extracts in a pH-dependent fashion with an optimum of pH 3-5. Acid proteinase activity was greater in mites raised on rabbits than in those raised on sheep. Inhibitors of cysteine, serine and metallo-proteinases failed to inhibit the hydrolysis of H-Pro-Thr-Glu-Phe-Phe(NO2)Arg-Leu-OH while pepstatin A, a specific inhibitor of aspartic proteinases, totally inhibited its hydrolysis at a concentration of 1 nM.