Amino acid sequence studies on the alpha chain of human fibrinogen. Characterization of 11 cyanogen bromide fragments.

The alpha chain of human fibrinogen consists of 600 +/- 25 amino acid residues, 10-11 of which are methionines. In this regard, we have identified and characterized 11 cyanogen bromide peptide fragments of 2, 3, 26, 28, 28, 37, 51, 56, 60 +/- 5, 64 +/- 5, and 260 +/- 20 residues, respectively. The sequences of five of these and a portion of a sixth have been reported previously. We now report the complete amino acid sequences of another of these fragments (56 residues), partial sequences for four others, and a preliminary characterization of the largest fragment. In a companion study (Doolittle, R. F., Cassman, K. G., Cottrell, B. A., Friezner, S. J., and Takagi, T. (1977), Biochemistry 16 (following paper in this issue)), we have obtained key overlap sequences from plasmic digests of fibrinogen which allow all but one of these cyanogen bromide peptides to be arranged in order. The sequences of some of these newly reported fragments have revealed an internal homology in the alpha chain, as well as structural similarities to the corresponding portions of the beta and gamma chains.