Human plasma fibrinogen heterogeneity: evidence for an extended carboxyl-terminal sequence in a normal gamma chain variant (gamma').

Abstract

Two types of normal human plasma fibrinogen, peak 1 and peak 2, are distinguishable by DEAE-cellulose gradient elution chromatography. The elution characteristics of peak 2 fibrinogen, which amounts to about 15% of the total, are attributable to the presence of a .gamma. chain variant, .gamma.'', which is more negatively charged than .gamma. chains and makes up about half of all such chains in that peak [Mosesson et al.]. Analyses of reduced S-carboxymethylated fibrin that had first been incubated in the presence of Factor XIIIa plus the fluorescent amine donor dansylcadaverine (DNScad) showed that the same amount of this compound could be incorporated covalently into either type of .gamma. chain. The DNScad-labeled COOH-terminal CNBr fragment (CNBr e) derived from the S-carboxymethylated .gamma. chain was smaller than the DNScad-labeled fragment (CNBr e'') from the .gamma.'' chain (Mr, 3200 and 4900) by about the same amount as the difference in size between the respective parent chains (Mr, 49,400 and 51,500). DNScad-CNBr e or DNScad-CNBr e'' could be further cleaved by trypsin to yield a smaller fluorescent fragment corresponding to the penultimate tryptic .gamma. chain peptide containing the DNScad-Gln acceptor and Lys donor crosslinking functions. The COOH-terminal amino acids of .gamma. and .gamma.'' chains were Val and Leu, respectively. The rates of Factor XIIIa-catalyzed crosslinking of peak 1 and peak 2 fibrin were the same, but peak 1 fibrin .gamma. chains formed only 1 species of crosslinked dimer (.gamma..gamma.) whereas peak 2 fibrin .gamma. chains yielded 3 (.gamma..gamma.,.gamma..gamma.'',.gamma.''.gamma.''). The .gamma.'' chains are functionally normal but have an extended COOH-terminal sequence accounting for their more negative charge and larger size relative to .gamma. chains.