AN INTERLOCKING SINGLE-STRAND MODEL FOR FIBRIN POLYMERIZATION.

The early stages of fibrin polymerization were investigated by rotatory shadowing and electron microscopy. Individual molecules within initial oligomers were found to be unaligned and contacted neighbouring molecules by single E + D and D + E contacts, suggesting an intermediate phase of activation (des A-fibrin). The interacting molecular domains were separated by a distance of 2 to 3 nm, indicating that (both or at least one) binding sites are located on protruding segments of the polypeptide chains. Upon completion of fibrin activation (des AA-fibrin), molecules within the early oligomers aligned to form single-stranded polymers,o these being characterized by repeating trinodular units of 230 A in length. Based upon these findings, a new interlocking single-stranded model for fibrin polymerization was designed and tested. The model is consistent with previous experimental data on fibrin polymerization such as that obtained by X-ray diffraction and negative staining. Moreover, early branching and lateral association phenomena are easily explained.