A comparative survey of the hydrolytic enzymes of ectoparasitic and free-living mites.

Extracts of ectoparasitic mites of birds (Dermanyssus gallinae), sheep (Psoroptes ovis) and plants (Tetranychus urticae) and of free-living mites (Acarus siro) contained acid and alkaline phosphatase, C4 and C8 esterases, lipase, leucine and valine aminopeptidases and a range of glycosidase activities. Dermanyssus gallinae and P. ovis, species highly adapted to an animal parasitic lifestyle, had very similar profiles and contained low activities of glycosidases. In contrast, the polyphagous species A. siro contained moderate to high activities of every glycosidase examined, whereas the phytophagous species, T. urticae, displayed high activities of only beta-galactosidase and beta-glucuronidase. All extracts hydrolysed haemoglobin with optima below pH6, and this hydrolysis was associated with an aspartic proteinase and variable cysteine proteinase activity dependent on species. Inhibitor-labelling with biotinyl-Phe-Ala-FMK revealed the presence of cysteine proteinases with molecular masses of 25-33.5kDa. Each mite species contains the enzymes necessary to complete digestion of the diet in the intracellular lysosomal compartment. The absolute and relative activities of each enzyme varied, and are discussed according to phylogeny and dietary habit.