title: Apyrase activity and platelet aggregation inhibitors in the tick Ornithodoros savignyi (Acari: Argasidae).
abstract: Ticks are ectoparasites that cause considerable damage to their hosts while feeding. The feeding process is facilitated by anti-haemostatic factors present in the tick saliva. Apyrase (ATP diphosphohydrolase, EC 3.6.1.5) is a platelet aggregation inhibitor found in most haematophagous organisms studied. The present study describes the identification and characterization of such an activity in the tick Ornithodoros savignyi. The enzyme conformed to many properties common to apyrases. These included a low substrate specificity, dependence on bivalent metal ions for activity and insensitivity to the classical ATPase inhibitors. Heat denaturation studies, pH optima and similar effects of inhibitors on the enzyme's ATP and ADP hydrolysing activitives supported its classification as an apyrase. Salivary gland extracts inhibited the platelet aggregation induced by ADP, collagen and thrombin and disaggregated aggregated platelets. The results suggest the presence of two or more anti-platelet factors present in the salivary glands of this tick species.
authors.affiliation: Department of Biochemistry, University of Pretoria, South Africa.
authors.forename: B J
authors.initials: BJ
authors.lastname: Mans
authors.forename: A R
authors.initials: AR
authors.lastname: Gaspar
authors.forename: A I
authors.initials: AI
authors.lastname: Louw
authors.forename: A W
authors.initials: AW
authors.lastname: Neitz
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001081:Apyrase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000032:analysis / Q000494:pharmacology*; D010976:Platelet Count; D011489:Protein Denaturation; D011506:Proteins / Q000032:analysis; D012469:Salivary Glands / Q000737:chemistry / Q000201:enzymology; D013379:Substrate Specificity; D013987:Ticks / Q000737:chemistry / Q000201:enzymology*
chemical_list: D002614:Chelating Agents; D004791:Enzyme Inhibitors; D010975:Platelet Aggregation Inhibitors; D011506:Proteins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D001081:Apyrase; D008274:Magnesium; D002118:Calcium; D004229:Dithiothreitol