Effect of monovalent cations on bovine alpha- and beta-thrombin: importance of substrate structure

The relative ability of bovine alpha- and beta-thrombin to hydrolyze selected anilide and ester substrates in presence and absence of monovalent cations has been evaluated. The hydrolysis of both TosGlyProArgpNA and H-D-PhePipArgpNA by either alpha-thrombin or beta-thrombin is more effective in the presence of 0.1 M NaCl than in the presence of 0.1 M KC1. The hydrolysis of BzArgpNA by alpha-thrombin was less effective in the presence of sodium ions than in the presence of potassium ions. The hydrolysis of this latter substrate by beta-thrombin was similar in the presence of either sodium ions or potassium ions. These results suggest that the ionic composition of the solvent affects that catalytic efficiency of alpha-thrombin and beta-thrombin in different ways dependent on the nature of the substrate.