Distribution of Prothymosin α in Rat Tissues

A radioimmunoassay, using a rabbit antiserum directed against thymosin α1, was employed to detect the presence of crossreacting peptides in rat tissues. Highest concentrations were present in thymus, but thymosin α1crossreacting material was also detected in brain, liver, kidney, lung, and spleen, in amounts ranging from 15% to 65% of the quantities found in thymus. In each case, the major immunoreactive peptide, after extraction and purification by a procedure that avoids proteolytic modification, was identified as prothymosin α , a peptide containing ≈ 112 amino acid residues. Prothymosin α is believed to be the endogenous peptide from which thymosin α1and other fragments are formed by proteolytic modification during the preparation of thymosin fraction 5. No peptides corresponding in size and chromatographic behavior to thymosin α1were detected with the extraction procedure employed.