[Antifibrinolytic effect of heparin]

The effect of heparin on non-stabilized fibrin hydrolysis by plasmin was investigated. Using analytical centrifugation in the presence of heparin, the existence of a high molecular weight fraction (sedimentation coefficient 17S) was demonstrated. Electrophoretic analysis revealed the presence of less degradable early, intermediate and late fibrin hydrolysis products. It is concluded that the molecular mechanisms of these effects are due to the direct action of heparin on the fibrin-monomer molecule which provides for the inhibition of peptide side chains localized between residues 15 Gly-53 Lys in the NH2-terminal part of the B beta-chain. The universal mechanisms underlying the anti-fibrinolytic activity of high molecular weight inhibitors of fibrin polymerization and aggregation are discussed.