Hydrolytic enzymes of Psoroptes cuniculi (Delafond)

Phosphatases, C4 and C8 esterases, leucine and valine aminopeptidases, N-ac etyl-beta-glucosaminidase, beta-glucosidase, beta-galactosidase and beta-gl ucuronidase were detected in extracts of the parasitic mite Psiriotes cunic uli. Lipase, trypsin-like and chymotrypsinlike activities were not present. Haemoglobin was hydrolysed by a detergent-soluble fraction of the mite ext racts with a maximum hydrolysis between pH 3 and 5. Acid proteinase activit y was greater against haemoglobin than bovine serum albumin. Inhibitors of cysteine, serine and metallo-proteinases failed to inhibit the hydrolysis o f H-Pro-Thr-Glu-Phe-Phe(NO2)-Arg-Leu-OH while pepstatin A inhibited its hyd rolysis in a dose-dependent manner (IC50 8.02 X 10(-11) M (+/- 0.30 X 10(-1 1)). Thermal inactivation of the proteolytic activity followed an exponenti al decay pattern. Typical K-m and V-max values were 7.2 x 10(-5) ( +/- 0.7 x 10(-5)) M-1 and 1.13 x 10(-3) ( +/- 0.05 x 10(-3)) OD unit(-1) min(-1) re spectively. Acid proteinase activity eluted from a size exclusion column in a single, major peak representing a molecular weight range of 21-24.5 kDa. The major endoproteinase of P. cuniculi therefore appears to be a cathepsi n D-like aspartic proteinase. (C) 1999 Elsevier Science Ltd. All rights res erved.