Apyrase from Embryo of the Camel Tick Hyalomma dromedarii

Apyrase is an enzyme that inhibits the aggregation of platelets by hydrolyzing the molecules ATP and ADP. Apyrase was purified from 18-days old embryos of the camel tick Hyalomma dromedarii and designated camel tick apyrase (CTA). The purification procedure involved anion exchange and gel filtration column chromatography. The purified CTA turned out to be homogeneous as judged by native polyacrylamide gel electrophoresis and its molecular weight was determined by gel filtration and SDS polyacrylamide gel electrophoresis to be 67 kDa. CTA displayed its maximum activity at pH 8.0 and cleaved preferentially ATP with Km value of 1.8 mM. CoCl2 and CaCl2 increased the activity of CTA while MnCl2, NiCl2, FeCl2 and ZnCl2 inhibited its activity. EDTA inhibits CTA noncompetitively with Ki value of 1.1 mM.