Abstract
An apyrase, ATP-diphosphohydrolase (EC 3.6.1.5) was purified from the soft tick, Ornithodoros savignyi. SDS–PAGE and native PAGE analysis, showed that tick apyrase has a molecular mass of 67 kDa and a basic iso-electric point. The purified enzyme conformed to properties associated with apyrases, including low substrate specificity, a dependence on bivalent metal ions and an insensitivity to normal ATPase inhibitors and sulfhydryl group reagents. It was, however, inhibited by chelating agents, mercuric chloride, dithiothreitol and fluoride. Mg 2+ had a stabilizing effect with respect to inactivation by DTT, suggesting that the enzyme is a metalloprotein. Compared to other apyrases, tick apyrase had higher kinetic rate constants (mM range). The enzyme also inhibited ADP- and collagen-, but not thrombin-induced platelet aggregation and disaggregated platelets that were aggregated by ADP. These properties indicate that apyrase fulfils an important function during tick feeding.
Published Version
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