[Mechanism of heparin inactivation by thromboplastin (factor III)]

Thromboplastin (a commercial one and that obtained from different tissues) is shown to inactivate heparin in proportion to the quantity of thromboplastin or to the heparin:thromboplastin ratio. A degree of inactivation of heparin changes after the modification of protein component of thromboplastin by proteases, however there is no dependence between the protein amount in the preparation and its antiheparin activity. Inactivation of heparin by thromboplastin is stipulated by the formation of associations due to electrostatic interactions between the clusters of amino acid protein residues (which dissociate under physiological conditions as bases) and heparin sulphogroups. It is suggested that factor III circulating in blood flow participates in the creation of hemostatic potential not only as a result of its ability to catalyze thrombinogenesis, but also due to the decrease of the anticoagulant blood activity.