| Abstract: |
Thymosin α1, an acidic 28-residue peptide, enhances immune function. We have described a radioimmunoassay for this thymic factor based on a rabbit antiserum raised against a thymosin α1-(15-28) conjugate (Incefy et al., J. Immun. Meth. 1986, in press). The detailed antigenic specificity of this antiserum was determined by measuring the ability of synthetic segments and analogues of thymosin α1 and related peptides to compete with radioiodinated Ac-Tyr-thymosin α1-(15-28) in this radioimmunoassay. The antiserum bound segments Ac-(1-28), (15-28), (20-28) and (21-28) with nearly equal efficiency but failed to bind segments Ac-(1-10), (11-20), (19-24) and (22-28). Thus, the major immunoreactive site seen by the antiserum is the COOH-terminal segment (21-28) (Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH). Immunoreactivity of (21-28) was nearly abolished when the carboxylate groups of Glu-21, Glu-27 and Asn-28 were omitted separately. The antiserum bound to prothymosin a and thymosin α11, which lack the α-carboxylate group of Asn-28, with 0.9 and 0.2%, respectively, of the efficiency of thymosin α1. But it bound nonspecifically to parathymosin α, which contains the internal segment ... -Glu-Val-Val-Glu-Glu-Glu-Glu-Asn- ... Residues Glu-21, Glu-27 and Asn-28 of thymosin α2 may be important features of the antigenic site through their ability to induce helical structure, through the ability of their negatively charged carboxylate groups to bind to specific sites on the antibody or both. © 1986. |
