Free radical-induced inhibition of ATP diphosphohydrolase activity (EC 3.6.1.5) from rat blood platelets.

In the present report we demonstrate the in vitro effects of free radicals on an ecto-ATP diphosphohydrolase activity (apyrase, EC 3.6.1.5) from rat blood platelets. Rat blood platelets were exposed to an oxidant-generating system (H2O2/Fe2+/ascorbate) and the ATP diphosphohydrolase activity was inhibited. The enzyme inhibition was prevented by glutathione (GSH) and cysteine but not by trolox as a vitamin E analogue. The TBARS (thiobarbituric acid reactive substances) assay and the determination of sulphydryl groups indicate that the inhibition of the enzyme activity in resting platelets is not related to lipid peroxidation or to oxidation of sulphydryl residues. These results demonstrate the susceptibility of ATP diphosphohydrolase activity from platelets to free radicals and suggest that amino acid residues which are essential for the enzyme function are probably modified.