Amino acid sequence studies on the α chain of human fibrinogen. Covalent structure of the α-chain portion of fragment D

Abstract

The .alpha.-chain portion of fragment D was purified from an exhaustive plasmic digest of human fibrinogen. The major polypeptide species has 91 amino acid residues, although a small amount of a 97-residue chain representing an earlier digestion stage remains. The amino acid sequence of the first 44 residues was determined by stepwise degradation with an automatic solid-phase sequencer. Another large stretch of sequence was revealed by the finding that the .alpha. chain of fragment D overlaps the cyanogen bromide fragments .alpha.CNIVA and .alpha.CNIII. The automatic sequencer results were confirmed and extended by the isolation and characterization of 18 of 19 expected tryptic peptides from the fragment D .alpha. chain. As a result, almost the entire sequence was obtained. The overlap with key cyanogen bromide fragments led to a proposal for an order for the first 198 residues of the fibrinogen .alpha. chain. A striking homology with the .gamma. chain and .beta. chain is apparent which has interesting structural implications.