Interaction of angiotensin peptides and zinc metal ions probed by electrospray ionization mass spectrometry.

Electrospray ionization-tandem mass spectrometry experiments were used to provide evidence regarding the sites of interactions between zinc metal ions and angiotensin peptides. The electrospray ionization mass spectra of histidine-containing human angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe) and angiotensin I (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu) in the presence of zinc show abundant multiply charged ions for the zinc-attached peptide [M + aZn(2+) +(c - 2a)H(+)](c+), where a = 1, 2 and c is charge. From collisionally activated dissociation experiments, with both low energy (triple quadrupole mass spectrometry) and high energy collisions (linked scan at constant B/E with a double focusing instrument) of the [M + Zn](2+) and [M + Zn + H](3+) ions for angiotensin II, a [b 6 + Zn](2+) species is produced as the most abundant product ion, suggesting that the zinc interaction site is in the vicinity of the His(6) residue. Additionally, tandem mass spectra from the zinc-attached ions for angiotensin I show abundant [b 6 + Zn](2+) and [b 9 + Zn](2+) products, providing evidence that both His(6) and His(9) are involved in zinc coordination.