PURIFICATION AND CHARACTERIZATION OF APYRASE FROM THE TICK, ORNITHODOROS-SAVIGNYI

An apyrase, ATP-diphosphohydrolase (EC 3.6.1.5) was purified from the soft tick, Ornithodoros savignyi. SDS-PAGE and native PAGE analysis, s howed that tick apyrase has a molecular mass of 67 kDa and a basic iso -electric point. The purified enzyme conformed to properties associate d with apyrases, including low substrate specificity, a dependence on bivalent metal ions and an insensitivity to normal ATPase inhibitors a nd sulfhydryl group reagents. It was, however, inhibited by chelating agents, mercuric chloride, dithiothreitol and fluoride. Mg2+ had a sta bilizing effect with respect to inactivation by DTT, suggesting that t he enzyme is a metalloprotein. Compared to other apyrases, tick apyras e had higher kinetic rate constants (mM range). The enzyme also inhibi ted ADP- and collagen-, but not thrombin-induced platelet aggregation and disaggregated platelets that were aggregated by ADP. These propert ies indicate that apyrase fulfils an important function during tick fe eding. (C) 1998 Published by Elsevier Science Inc. All rights reserved .