Fibrin subunits in venous and arterial thromboembolism

The subunit fibrin composition of thrombi of both venous and arterial origin was examined by sodium dodecyl sulphate gel electrophoresis. The thrombi were recovered by surgical intervention and all had the same fibrin subunit composition. The alpha chains were cross-linked as alpha-chain polymers alpha (p), the gamma chains as gamma-chain dimers (gamma-gamma) while the beta chains were not crosslinked; a further subunit of molecular weight 33 000 was shown to be present in all the fibrins examined and was a degradation fragment of the beta or gamma chains. This data suggests that the crosslinked alpha chains are rate limiting to the lysis of thrombi in vivo. The digestion of pulmonary emboli by plasmin yielded soluble degradation products which were identified as D dimer and E, the latter fragments being the major products obtained by the lysis of in-vitro made plasma clots. The similarity of the composition and lysis of thrombus fibrin to that formed in vitro augurs well for the justification of in-vitro research on mechanisms in thrombolysis.