Effects of crosslinking on the rigidity and proteolytic susceptibility of human fibrin clots

Clots formed in reconstituted human plasma or from purified human fibrin were studied in order to assess the effects of subunit crosslinking on clot strength and on resistance to plasmin degradation. The relative amounts of a chain and γ chain ligation were varied by adding factor XIII to the samples. We observe, as have others, that appreciable γ - γ crosslinking always precedes detectable formation of α dimer or α polymer. Non-invasive light scattering measurements of the shear modulus G(t) indicate that ligation of γ chains and of α chains have qualitatively similar effects on clot strength. Since α crosslinking occurs very slowly in the clots which are formed from plasma, we infer that under physiological conditions the involvement of α chains in the development of clot strength probably is only a secondary function. Light scattering techniques also were used to study the size of particles shed from the surfaces of fibrin clots undergoing fibrinolysis, and no differences could be discerned as resulting from ligation of α chains.