Amino acid composition of human fibrinogen and anticoagulant derivatives

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Abstract
The amino acid compositions of human fibrinogen and 3 intermediate anticoagulant derivatives were determined by column chromatography. The derivatives were isolated by ammonium sulfate fractionation and column electrophoresis from solutions of fibrinogen undergoing spontaneous breakdown. One derivative, isolated as the large electrophoretic peak at the end of the clottable period (100% CP) of the parent fibrinogen solution, was labelled LP100 and others obtained at twice this period (200% CP) were designated as LP200 and SP200 (LP, large peak; SP, small peak). Maximal molecular weights of approx. 294000 for LP100, 137000 for LP200 and,37000 for SP200 were calculated for the protein moieties. At least 265 amino acid residues must have been lost from each fibrinogen molecule during the formation of LP100, and 1362 during the formation of the other 2 derivatives. Only I derivative (LP200) had a partial specific volume ([image] 0.725 ml/g) different from that of fibrinogen ([image] 0.721 ml/g). No significant differences in refractive index at 589 m[mu] were detected. Calculation of the total number of ionizable groups /105g of each protein moiety showed a preponderance of the following numbers of negative charges: 22 in fibrinogen; 24 in LP100; 26 in LP200; 49 in SP200. The isoionic points were estimated to be approx. + 0.03 pH unit (for fibrinogen), [long dash]0.06pH unit for (LP100) and + 0.28 pH unit for (LP200) from the pK of imidazole, and 0.78 pH unit above the average pK of aspartyl and glutamyl ions (for SP200). These figures agree closely with experimentally determined values of the isoelectric point of fibrinogen and its derivatives.