Acetylation of antithrombin III by aspirin

Although the effect of aspirin in blood coagulation has been believed to be due to its ability to interfere with platelet function, very few studies have reported its effect on various blood coagulation proteins. Since aspirin (acetylsalicylic acid) is known to acetylate numerous biologic macromolecules, the effect of aspirin on antithrombin III was investigated. It was found that antithrombin III is irreversibly inactivated by treatment with aspirin. The inactivation follows pseudo first-order kinetics and incorporation of one molecule of aspirin per molecule of the protein is necessary for complete inactivation. Reaction with acetyl-[14C]-salicylic acid incorporated 1.4 mol of acetyl group per mole of protein but reaction with carboxyl-[14C]-acetyl salicylic acid incorporated only 0.03 mol of radioactive label per mole of the protein. Furthermore, sodium salicylate does not inactivate the protein. This suggests that the reaction occurs through the acetylation of antithrombin III. Amino group analysis of aspirin-treated antithrombin III using trinitrobenzenesulfonic acid revealed that one to two primary amino groups are lost relative to the untreated antithrombin III. It is concluded that the reaction of aspirin with antithrombin III results in specific acetylation of lysine residues.