Amino acid sequence studies on the .alpha. chain of human fibrinogen. Overlapping sequences providing the complete sequence

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Abstract
The complete amino acid sequence of the .alpha. chain of human fibrinogen was determined. It contains 610 amino acid residues and had a calculated MW of 66,124. The chain had 10 methionines, and fragmentation with cyanogen bromide yielded 11 peptides. The arrangement of the 11 fragments was determined by the isolation of peptide overlaps from plasmic and staphylococcal protease digests of fibrinogen and/or .alpha. chains. Certain cyanogen bromide fragments, preliminary reports of whose sequences appeared previously, were reexamined in order to resolve several discrepancies. The .alpha. chain was homologous with the .beta. and .gamma. chain of fibrinogen, although a large repetitive segment of unusual composition was absent from the latter 2 chains. Existence of this unusual segment divides the sequence of the .alpha. chain into 3 zones of about 200 residues each that were readily distinguishable on the basis of amino acid composition alone.