Chemical synthesis of a peptide fragment of thymopoietin II that induces selective T cell differentiation.

Thymopoietin is a polypeptide hormone of the thymus that consists of a 49 amino acid polypeptide chain of 5562 daltons. A peptide corresponding to positions 29-41 of bovine thymopoietin II was synthesized by the Merrifield solid-phase technique. This peptide was shown to have a purity (correct sequence) of 96% by amino acid and C terminal analyses and by a complete determination of the amino acid sequence by manual Edman degradations. It displayed a selectivity of action similar to that of thymopoietin itself, inducing the differentiation of T lymphocytes but not of complement receptor (CR+) B lymphocytes. Although a number of substances induce the differentiation of both T cells and CR+B cells under the conditions of assay in vitro, only thymopoietin and the synthetic peptide described in this report have been shown to induce the differentiation of T cells selectively. Our data establish that the key residues involved in the active site of thymopoietin are present within a synthetic polypeptide which constitutes a minor portion of the amino acid sequence of thymopoietin. Since this peptide had 3% activity by comparison with thymopoietin, the tertiary structure of thymopoietin may be required for optimal configuration of the active site to produce full biological activity.