The Gd3+-induced perturbations in the NMR spectra of a cell differentiating peptide fragment, ArgLysAspValTyr (TP5), have been examined. This pentapeptide fragment retains the selective T-cell differentiating activity of its parent polypeptide thymic hormone, thymopoietin. The observed relaxation enhancements induced by Gd3+ have been analyzed to determine the relative and absolute amide and aromatic proton-Gd3+ distances. The data are compatible with a bidentate model, in which both the aspartyl and tyrosyl carboxylates bind the metal ion simultaneously in a chelate fashion, being the dominant conformer. From these studies a picture of the conformation of Ln3+ complexes of TP5 begins to emerge. © 1982.
