Structural and chromatographic heterogeneity of normal plasma fibrinogen associated with the presence of three gamma-chain types with distinct molecular weights.

Three different gamma chains have been identified in fibrinogen isolated from normal human plasma with apparent molecular weights of 50000 (gamma 50), 55000 (gamma 55) and 57500 (gamma 57.5), as shown by SDS-polyacrylamide gel electrophoresis. Plasma fibrinogen was separated by ion-exchange chromatography on DEAE-Sephacel into three populations of molecules, each differing in gamma-chain composition. The first peak contained 87% of the total fibrinogen and was composed of molecules containing only gamma 50 chains; the second peak included 3% of the fibrinogen and contained one gamma 50 and one gamma 55 chain, and the third peak had 10% of the total which contained one gamma 50 and one gamma 57.5 chain. Cross-linked fibrin obtained from fibrinogen with only gamma 50 chains contained gamma gamma dimers exclusively of Mr 100000, representing a uniform gamma 50 gamma 50 dimer composition. The gamma gamma dimers from purified fibrinogen of gamma 50 gamma 55 type had molecular weights of 111000, 105000 and 100000, while dimers from gamma 50 gamma 57.5 fibrinogen were of Mr 115000, 108000 and 100000. The relative proportions of gamma gamma dimers from each purified fibrinogen population were consistent with random crosslinking of the gamma monomers. The gamma-chain identity of the variants was established by their conversion to covalent dimeric species after clotting by thrombin in the presence of Factor XIII, their incorporation of the fluorescent lysine analog dansyl cadaverine, by the staining intensity of monomeric and dimeric forms with the periodic acid-Schiff reagent after electrophoretic separation, and by plasmic degradation of all monomeric and dimeric forms in a pattern that was characteristic for gamma chains. Individual gamma gamma dimers were purified by preparative gel electrophoresis, and tyrosine was demonstrated to be the amino-terminal residue of all three gamma chain types. We conclude that normal human fibrinogen can be separated into three populations of molecules due to molecular weight heterogeneity of their gamma chains.