Structural study of circulating thymic factor: a peptide isolated from pig serum. II. Amino acid sequence.

The amino acid sequence of a circulating thymic factor (FTS, facteur thymique sérique) isolated from pig serum has been established as less than Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn-OH. This sequence was obtained by Edman analysis both on the intact peptide and after tryptic digestion. The COOH-terminal residue was identified by carboxypeptidase A digestion. A synthetic peptide was prepared which showed the same biological activities as native pig circulating thymic factor, thus confirming the proposed primary structure.