Metal‐peptide interactions: enkephalin rigidifications

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Abstract
Two enkephalin analogs, Tyr-D-Ala-Gly-Phe-NVal-NH2 and Tyr-D-Ala-Gly-Phe-NVal-OH, were studied by NMR spectroscopy. 13C chemical shifts were determined as a function of pH and in water-dimethyl sulfoxide solvent mixtures. The acid and amide forms of the analogs show a marked difference in their NMR features. Complexation with metal ions causes changes in the NMR spectra of the acid form. The temperature dependence of the NH proton resonances of the Zn complex shows striking similarity with that of the amide analog. The results are discussed in terms of the potential modification of biological activities which may occur following metal ion induced conformation changes.