Structural difference between polymerized and non-polymerized fragment X, obtained by plasmin digest of fibrinogen.

Fragment X (LMrFX) was obtained as low molecular weight preparations from a late stage 2 plasmin digest of human fibrinogen. The thrombin-treated LMrFX preparations, which resulted in impaired polymerization, were further subfractionated into polymerized and non-polymerized components. The fractions were examined by SDS-PAGE and immunochemical methods. In polymerized fractions, more peptide bands were observed on SDS-PAGE in the reduced state than in non-polymerized fractions. Both fractions contained a similar number of internal cleavages in the A alpha, B beta and gamma chains, which are linked by disulfide bonds. Thus, the partial deficiencies in polymerization sites of the carboxy terminal region of the gamma chain and the amino terminal portions of the B beta chain, as well as internal cleavage, were considered to participate in the impairment of the thrombin-induced polymerization of LMrFX.