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

The complete amino acid sequence of the alpha chain of human fibrinogen has been determined. It contains 610 amino acid residues and has a calculated molecular weight of 66,124. The chain has 10 methionines, and fragmentation with cyanogen bromide yields 11 peptides [Doolittle, R.F., Cassman, K.G., Cottrell, B.A., Friezner, S.J., Hucko, J.T., & Takagi, T. (1977) Biochemistry 16, 1703]. 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. In addition, certain of the cyanogen bromide fragments, preliminary reports of whose sequences have appeared previously, have been reexamined in order to resolve several discrepancies. The alpha chain is homologous with the beta and gamma chains of fibrinogen, although a large repetitive segment of unusual composition is absent from the latter two chains. The existence of this unusual segment divides the sequence of the alpha chain into three zones of about 200 residues each that are readily distinguishable on the basis of amino acid composition alone.