Synthetic analog of the thymosin_α1 fragment 24–28 alters the coagulating and aggregating activities of α-thrombin

Abstract

A pentapeptide (EEAEN), which is the 24–28 fragment of the COOH-terminal sequence in the thymosin_α1 molecule highly homologous with the 54–58 region of hirudin (with the complementary anion-binding exosite in the thrombin molecule), was synthesized by a solid-phase method. Preincubation of α-thrombin with EEAEN in concentrations of 0.1 pM to 1 nM reduced its clotting activity while preincubation of this enzyme with EEAEN in concentrations of 0.01 to 1 nM reduced its platelet-aggregating activity. The reaction of EEAEN with thrombin is shown to be similar to the reaction of the entire thymosin_α1 molecule. It is concluded that the COOH-terminal thymosin_α1 peptide EEAEN may be the reactive site responsible for the antithrombin activity of thymosin_α1.