Altered inactivation of trinitrophenylated thrombin by antithrombin iii in the presence of heparin

Modification of bovine α-thrombin by exposure to 2,4,6-trinitrobenzenesulphonic acid and the effects of the modification on the inactivation of the enzyme in the presence of heparin are reported. Transformation of four-five lysine residues resulted in a decrease of the clotting activity of the enzyme by 30–40%, yet its interaction with antithrombin III was not significantly impaired. However, the catalytic effect of heparin on the thrombin-antithrombin III reaction was grossly reduced and the potentiating effects of NaCl and CaC12 on heparin-mediated catalysis was either minimized or no longer apparent.