Co-ordination of nickel(II) ions by angiotensin II and its peptide fragments. A potentiometric, proton nuclear magnetic resonance and circular dichroism spectroscopic study

Abstract

A potentiometric and spectroscopic (n.m.r., circular dichroism, and u.v.–visible) study of the complexes of angiotensin II and two of its peptide fragments, Asp-Arg-Val-Tyr and MeCO-Tyr-IIe-His, with Ni^II has been undertaken. The results show that, above pH 8, Ni^II co-ordinates to four nitrogen donors starting at the terminal amino nitrogen of the aspartyl residue to form a diamagnetic, planar complex. Co-ordination through the imidazole N of the histidyl residue may be present below pH 8–9 but is absent at high pH. The high-resolution ¹H n.m.r. spectrum of angiotensin II and of its nickel(II) complex at pH 11 have been recorded and the side-chain resonances assigned.