The Interaction Between Heparin and Plasmin on Amidolysis

Inhibition of plasmin activity by sulfated polyvinylalcohol-acrylate copolymers

The effect of four sulfated polyvinylalcohol-acrylate copolymers and heparin on plasminogen activation and on plasmin activity is studied. The molecules differing in charge (proportion of negatively charged units 40.5%-73.5% of the total) and in size (5600 Da-8800 Da) accelerate plasminogen activation by 2- up to 4-fold at a 7-fold molar excess of the polyvinylacrylates over plasminogen. They, however, exert a concentration and charge-dependent effect on plasmin: both the amidolytic (half-maximal effect at a 1.33-3.66 molar excess of the polyvinylacrylates) and fibrinolytic (half-maximal effect at 1.23-1.72 molar excess of the polyvinylacrylates) activities of plasmin are inhibited. In contrast, heparin (a similarly carboxylated and sulfated polymer) and polyvinylacrylates with a low number of sulfate groups (30% sulfated monomers) at concentrations up to 2.2 microM do not affect plasminogen activation and plasmin activity in a milieu of physiological ionic strength. Experiments with plasmin derivatives lacking N-terminal peptides of different length (des-kringle(1-4) and des-kringle(1-5) plasmin) show identical changes in the protease activities, precluding involvement of the kringle-domain in the interaction with the polyvinylacrylates. Fluorescence studies evidence the charge-dependent binding of the polyvinylacrylates to plasmin, but not to plasminogen. Thus, through non-covalent interaction with the protease-domain of plasmin the polyvinylacrylates inhibit fibrinolysis. Since these sulfated copolymers inhibit both thrombin [4] and plasmin activity, they may be a useful therapeutic tool in situations when both the blood coagulation and the fibrinolytic system are activated (such as intravascular coagulation and fibrinolysis, ICF).

Co-immobilization and interaction of heparin and plasmin on collageno-elastic tubes

Heparin and plasmin were co-immobilized on collageno-elastic tubes (CETs) in order to develop a thromboresistant and fibrinolytic vascular prosthesis. The mutual interaction between heparin and plasmin both in the soluble and in the immobilized state was studied. The immobilization condition rendering maximum co-immobilized heparin and plasmin activity was identified to require heparin immobilization followed by plasmin immobilization. Soluble heparin exerts a positive synergistic effect on soluble plasmin. Immobilized heparin enhances plasmin loading on the CET as compared to the heparin-free graft. Heparin, in both the soluble or immobilized state, significantly decreases the Michaelis-Menten (M-M) parameter Km for immobilized plasmin over heparin-free immobilized plasmin. Furthermore, the M-M parameter Vmax for the immobilized plasmin in the presence of heparin decreases over heparin-free immobilized plasmin. These results suggest a decrease in the kinetic constant k3 for heparin-modified immobilized plasmin over the heparin-free form. Co-immobilized heparin-plasmin collagenous grafts represent a unique advance in the development of fibrinolytically active prostheses.