The effect of monovalent cations on the catalytic activity of thrombin

The effect of monovalent cations on the catalytic action of thrombin has been examined utilizing a variety of substrates. Sodium chloride noncompetitively inhibited the action of thrombin on α-tosyl-l-arginine methyl ester and α-N-benzoyl-l-arginine-p-nitroanilide. No inhibition was noted when α-N-benzoyl-l-arginine ethyl ester was the substrate. The extent of inhibition was considerably less with either potassium chloride or lithium chloride. The rate of inactivation of thrombin by 1-chloro-3-tosylamido-7-amino-l-2-heptanone was reduced in the presence of sodium ions. The results are interpreted to show a specific effect of sodium ions on the ability of the active-site histidine residue to participate in thrombic catalysis.