AMINO-ACID SEQUENCE STUDIES ON THE ALPHA-CHAIN OF HUMAN-FIBRINOGEN - COMPLETE SEQUENCE OF THE LARGEST CYANOGEN-BROMIDE FRAGMENT

The largest fragment produced by complete cyanogen bromide digestion of the α chain of human fibrinogen contains 236 residues and has a calculated molecular weight of 23 949. The complete amino acid sequence of the fragment was determined by the isolation of peptides generated by plasmin, trypsin (including digestion of citraconylated material), staphylococcal protease, and chymotrypsin. In addition, some key subfragmentation was achieved by selective chemical cleavage at tryptophan residues. The fragment has an unusual amino acid composition, more than half of its residues being glycine, serine, threonine, and proline. There are very few nonpolar residues, although 7 of the α-chain's 10 tryptophans occur in this fragment. The fragment contains 2 cysteine residues located 30 residues apart which are connected by an intrachain disulfide bond in the native molecule. The tryptophans occur with a definite periodicity that highlights a series of 13-residue homology repeats. The fragment also contains the two principal α-chain cross-linking sites. © 1979, American Chemical Society. All rights reserved.