Proton nuclear magnetic resonance study of the biologically active peptide analog [Pro2]thymopentin

The solution conformation of the pentapeptide Arg‐Pro‐Asp‐Val‐Tyr ([Pro2]TP5), a biologically active analog of the immuno‐regulatory peptide thymopentin, Arg‐Lys‐Asp‐Val‐Tyr (TP5), was investigated by proton nuclear magnetic resonance spectroscopy. The chemical shift variations with pH, the vicinal coupling constants and the amide hydrogen exchange rates were measured. The hydrogen exchange rates for Val4 NH and Tyr5 NH are more than six times slower than the predicted values for the corresponding solyated peptides. The guanidino NaH proton of the Arg1 residue shows a downfield shift with a pKa of 3.5 as the pH is increased. The conformational properties of [Pro2]‐thymopentin were compared with those of two other closely related immunoregulatory peptides, thymopentin and [Glu3]TP5 (SP5).