Structure and immunological properties of thymosin β₉ Met, a new analog of thymosin β₄ isolated from porcine thymus

During the course for the studies of thymosin β₄ and prothymosin α from porcine thymus, a new analog of thymosin β₄ has been identified. This peptide consists of 41 amino acid residues. The amino terminus is blocked by an acetyl group as revealed by fast atom bombardment mass spectrometric analysis. Amino acid sequence studies disclosed that this peptide is identical to bovine thymosin β₉ except that leucine at position 6 in β₉ is substituted by methionine. Thus, this new peptide has been termed thymosin β₉ Met. The recoveries of β₉Met, β₄, and prothymosin α in porcine tissues have been determined (in μg/g tissue) as follows: thymus (43, 85, 133); spleen (68, 203, 37); liver (10, 31, 27); heart (1.5, 10, 0); kidney (5, 51, 37); brain (0.8, 31, 5). Biologically, thymosin β₉ Met was found to be more active than β₄ in enhancing γ‐interferon production in cord blood lymphocytes. However, β₄ appeared to stimulate higher amounts of interleukin 2 and tumor necrotic factor. The significance for the coexistence of two homologous peptides with similar functions in the thymus and a number of other organs is not clear, and deserves further investigation.