The molecular weights, mass distribution, chain composition, and structureof soluble fibrin degradation products released from a fibrin clot perfused with plasmin

We used a perfused clot system to study the degradation of cross-linked fib rin, Multiangle laser light scattering showed that plasmin-mediated cleavag e caused the release of noncovalently associated fibrin degradation product s (FDPs) with a weight-averaged molar mass (M-w) of similar to 6 x 10(6) g/ mol. The M-w of FDPs is dependent on ionic strength, and the M-w observed a t 0.15 M NaCl resulted from the self-association of FDPs having M, of simil ar to 3.8 x 10(6) g/mol. Complete solubilization required the cleavage of s imilar to 25% of fragment D/fragment E connections, with 48% alpha-, 62% be ta-, and 42% gamma-chains cleaved. These results showed that D-E cleavage c annot be explained by a random mechanism, implying cooperativity. Gel filtr ation and multiangle laser light scattering showed that FDPs range from 2.5 x 10(5) to 1 x 10(7) g/mol. In addition to fragment E, FDPs are composed o f fragments ranging from 2 x 10(5) Da (D-dimer, or DD) to at least 2.3 x 10 (6) Da (DX8D). FDP mass distribution is consistent with a model whereby FDP s bind to fibrin with affinities proportional to fragment mass. Root mean s quare radius analysis showed that small FDPs approximate rigid rods, but th is relationship breaks down as FDPs size increases, suggesting that large F DPs possess significant flexibility.