Metal lon Effects on the cis/trans lsomerization Equilibrium of Proline in Short-Chain Peptides:A Solution NMR Study

摘要

The effect of copper(11) ions on the probabilities of existence of the four detectable conformers of the tetrapeptide Tyr-Pro-Phe-Pro(#beta#-casomorphin 4)in [2~H_6]DMSO was investigated by 1~H NMR spec-troscopy.Integration of the Phe-NH signals provided the relative populations in the free state as tt/tc/ct/cc=28:34:29:9 at 293K(c=cis,t=trans).Copper(11)was shown to bind to all four isomers yielding complexes with two different structures ,depending on the conformation of pro~2.The interpretation of paramagnetic relaxa-tion rates of pro~2-h#alpha# signals provided the corresponding isomeric probabilities in the metal-bound state as 13:36:20:31.The observed stabilization of the conformation with the lowest probability of existence (cc) may be relevant for the biological role of copper and other metal ions.