Isolation and structural characterization of thymosin-β₄ from a human medullary thyroid carcinoma

An extract of a tumour metastases from a human medullary thyroid carcinoma contained a high concentration (at least 2.9 nmol/g wet weight) of the immunoregulatory peptide, thymosin-β₄. The peptide was isolated as a mixture of two components with free and blocked NH₂-terminal amino acid residues, the latter form predominating (approximately 98% of the total). The primary structure of the peptide was established by automated Edman degradation after cleavage with cyanogen bromide. The amino acid sequence of human thymosin-β₄ was identical to thymosin-β₄ previously isolated from calf thymus. Further studies are warranted to determine whether thymosin-β₄ production is a useful marker for thyroid and other tumours.