Fibrinogen fraction I (340 kDa) and fraction II (305 kDa) were isolated by glycine precipitation. The subunit chains of the two fractions were separated, after reduction, by reverse-phase high performance liquid chromatography. The amino acid compositions of the Bβ and τ chains of fibrinogen II were identical with those of fibrinogen I. In contrast, the Aα chains of fibrinogen II were composed of two populations, one comprising homogeneous, intact Aα chains and the other consisting of heterogeneous, deficient Aα chains (Aα' chains) of lengths varying according to the sizes of their COOH-terminal defects. The molar ratio of the Aα to the Aα' chains in fibrinogen II was 1.16:1. The amino acid composition and sequence analyses of the TPCK-trypsin peptides derived from the Aα' chains revealed that the COOH-terminal residues of the Aα' chains were mainly Asn-269, Gly-297 and Pro-309. These results indicate that the fibrinogen II molecule is asymmetrical and can be represented by the formula (Aα)(Aα')(Bβ)2(τ)2 and that fibrinogen II cannot be a plasmin degradation product of fibrinogen I.
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