Gene action in the human haptoglobins. IV. Amino acid sequence studies on the haptoglobin α chains

Alpha chains of human haptoglobin have been prepared from whole haptoglobin of genetic type Hp 2–1 purified from the ascites fluid of a single patient. Amino acid sequence analysis has been carried out on these light chains which represent the products α1S and α2(F,S) of the single genes Hp1S and Hp2(F,S), and are, respectively, 83 and 142 residues in length. The data reported here concern the sequence analysis of two series of tryptic peptides, one obtained by unlimited cleavage of the chains by p-toluene sulfonamido-phenylethyl chloromethyl ketone - trypsin, and the second following limitation of trypsin cleavage to arginyl residues after modification of lysyl residues by trifluoracetylation. The major technique for sequence analysis of these peptides was a modification of the p-dimethylaminonaphthalene-sulfonyl-Edman (dansyl-Edman) procedure employing a new thin-layer chromatographic separation of the dansyl-amino acids. The sequences of these tryptic peptides in conjunction with those of the chymotryptic peptides allowed the unequivocal deduction of portions of the sequence, but the final overlaps were provided by fragments obtained by specific chemical cleavage of the chain at aspartyl residues. The amino acid sequences deduced have documented the occurrence of a partial gene duplication in the gene product α2(F,S) of the Hp2(F,S) gene.