Research Article| Volume 70, ISSUE 1, P106-115, July 1967

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Effects of reptilase and thrombin on human blood platelets and observations on the molecular mechanism of clot retraction

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      Reptilase, an extract from the venom of Bothrops jararaca, like thrombin, clotted platelet fibrinogen, produced platelet aggregation, and released intraplatelet serotonin and adenine nucleotides. In contrast to thrombin, reptilase produced loose, easily disrupted platelet aggregates, and reptilase-induced clots of purified fibrinogen did not retract. Clot retraction occurred only when plasma was added to the system. Degradation of adenine nucleotides of platelets during clotting of fibrinogen induced by reptilase resulted in a marked decrease in ATP and ADP and an increase in AMP and adenosine, whereas thrombin produced an increase in ADP as ATP was degraded. When plasma was used in place of fibrinogen in these experiments, degradation of the adenine nucleotides was similar regardless of whether thrombin or reptilase was used to induce clot retraction. Reptilase previously has been shown to release only peptide A from fibrinogen while thrombin, splits off two fibrinopeptides, A and B. Accordingly, the removal of peptide A and B from fibrinogen may be required to permit clot retraction to occur. Since reptilase, unlike thrombin, does not cause viscous metamorphosis (fusion) of platelets nor the production of ADP, the differing retraction promoting effects of the two enzymes, at least in, part, may be attributable to their differing actions on platelets. Platelets react to numerous proteolytic enzymes among which thrombin is unique in its ability to induce viscous metamorphosis and clot retraction.
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