INHIBITION BY AJOENE OF PROTEIN-TYROSINE-PHOSPHATASE ACTIVITY IN HUMAN PLATELETS

The effects of ajoene (a potent antithrombotic agent obtained from gar lic) on the tyrosine phosphorylation status of human platelet proteins were investigated by immunoblotting-based experiments using an anti-p hosphotyrosine antibody. Incubation of platelets with ajoene enhanced the phosphorylation of at least four proteins (estimated MWs 76, 80, 8 4 and 120 kDa), both in resting platelets and in platelets subsequentl y stimulated with thrombin (0.1 U/ml), This effect was both dose- and incubation-time-dependent. High concentrations of ajoene (50 mu M) or long periods of incubation (10 min) led to nonselective 'hyperphosphor ylation' of numerous proteins. The effects of ajoene on protein tyrosi ne phosphatase (PTP) activity in platelet lysates were also investigat ed. PTP activity was inhibited when platelets were incubated with ajoe ne before lysis, but not when ajoene was added to lysates of platelets which had not been pre-exposed to ajoene.