The interaction of heparin with human plasmin

1. The interaction of heparin with human plasmin was investigated measuring plasmin activity and enzyme inactivation in the presence of heparin. Hydrolysis of synthetic substrates (H-D-Val-Leu-Lys-pNA, H-D-Val-Phe-Lys-pNA and H-D-Pro-Phe-Lys-pNA) by plasmin was enhanced by heparin through an increase in kcat values. 2. This effect was the consequence of a change of Vmax since Km values were not altered in the presence of heparin. The polysaccharide also enhanced the rate of enzyme inactivation using TLCK as an active site blocking reagent. 3. Furthermore, heparin increased the heat sensitivity of plasmin, when synthetic substrate H-D-Val-Leu-Lys-pNA was used but it did not affect enzyme activity towards N-benzoyl-L-arginine-ethylester substrate. 4. The data show that microenvironmental conformation around the active center of plasmin is influenced by heparin.