The amino-acid sequences of three cystine-free cyanogen-bromide fragments of human serum transferrin.

The amino acid sequences of three fragments obtained on cyanogen bromide cleavage of human transferrin have been determined. Two of the fragments are small (4 and 7 residues) and had not been isolated in previous studies of the CNBr fragments of transferrin. The sequence of the larger fragment (53 residues) was elucidated by examining peptides isolated from digests of the fragment with trypsin, chymotrypsin or thermolysin. This region of transferrin appears to contain the sites of three previously-reported substitutions in the D1 and D-chi genetic variants.