The Lanthanides as Structural Probes in Peptides

We have been interested in developing a methodology based on the analysis of paramagnetic lanthanide ion perturbations observed in the NMR parameters of the peptide. One of the apparent limitations of this approach is the fact that in aqueous solution the peptide must contain a suitable metal ion binding site. Recently we have been able to show, however, that a relatively minor chemical modification of a neurohypophyseal hormone (oxytocin) produced a metal ion binding derivative (1). In the present communication we will discuss the results of NMR experiments performed on two peptides as an illustration of our approach. These peptides are angiotensin II, (Asp-Arg- Val-Tyr-Ile-His-Pro-Phe) a hormone which contains a metal ion binding site and [Glu4]-oxytocin $$ \left( {{\text{oxytocin}} \equiv {\text{Cys - Tyr - Ile - Gln - Asn - Cys - Pro - Leu - Gly - N}}{{\text{H}}_{\text{2}}}} \right) $$ .