Ionophoric properties of angiotensin II peptides. Nuclear magnetic resonance kinetic studies of the hormone-mediated transport of manganese ions across phosphatidylcholine bilayers

Abstract

The linear peptide hormones angiotensin II and [Asn1, Val5]angiotensin II are found to mediate the transport of Mn(II) ions across phosphatidylcholine bilayers. Nuclear magnetic resonance spectroscopy (NMR) is applied to monitor the rate of transport of Mn(II) ions by measuring the rate of disappearance of the 1H NMR signal of the choline methyl groups of the inner phospholipid layer. This rate of disappearance is analyzed in terms of a pseudo-first-order rate equation for the transport process. The rate of transport of Mn(II) varies linearly with both the concentrations of Mn(II) and agiotensin II (A-II) present, suggesting that the ions are transported in a complex with 1:1 stoichiometry. An analysis of the temperature dependence of the rate of transport yielded an energy of activation of 29 +/- 5 kcal/mol and an entrophy of activation of 10 eu for the transport process. The activation parameters are discussed in terms of defining the rate-limiting step in the transport process. The pH dependence of the hormone-mediated rate of Mn(II) transport is similar to the pH dependence of the metal complexation process measured in a separate study. The presence of La(III) or Tris decelerates the rate of Mn(II) transport by presumably competing with either Mn(II) or A-II, respectively, in the binding process. On the basis of the results presented here as well as literature data, we suggest that the ionophoric properties of these two hormones may be relevant to understanding the role of metal ions in their physiological activities.

Nickel Ion Complexes of Amino Acids and Peptides

“…Angiotensin II, a peptide hormone which has the sequence Asp-Arg-Val-TyrIle-His-Pro-Phe, is involved in the regulation of blood pressure and has been shown to interact with metal ions in biological systems [178]. The study of the complexes of angiotensin II and two of its peptide fragments, Asp-Arg-Val-Tyrand MeCO-Tyr-Ile-His, with Ni(II) shows that metal ions at high pH form 4N species with the metal ion bound at the N-terminus of angiotensin II, giving a complex closely similar to that formed by Asp-Arg-Val-Tyr [85].…”

Time-Dependent Interactions of the Two Porphyrinic Compounds Chlorin e6 and Mono-l-aspartyl-chlorin e6 with Phospholipid Vesicles Probed by NMR Spectroscopy

“…In this paper, unilamellar phospholipid bilayer vesicles of intermediate size (50−60 nm in diameter) formed from 1,2-dioleoyl-phosphatidylcholine (DOPC, Figure ) were used as model membranes. Owing to their dynamic properties, these vesicles provide membrane mimicking systems well suited for NMR spectroscopic investigations in the solution state, giving rise to sufficiently well-resolved isotropic lines. , NMR studies have been successfully applied to study the transport of various compounds across such lipid bilayer membranes or to investigate factors modulating membrane permeability. − Usually, NMR signals of the incorporated compound have been evaluated for this purpose, partially with the aid of paramagnetic shift reagents, − or the membrane permeability for paramagnetic metal ions was monitored by analyzing temporal changes of inner and outer phospholipid (PL) NMR signals induced by the paramagnetic effect of the nearby metal ions. , Even though the NMR investigation of kinetics is restricted to slow processes, our studies demonstrate that the NMR spectroscopic approach can provide comprehensive information on the membrane localization and transfer of porphyrinic compounds. The method takes advantage of the large porphyrin ring current effects inducing major shift and line width changes to the NMR signals of PL molecules in spatial proximity.…”

X-537A ionophore-mediated calcium transport and calcium phosphate formation in pressman cells

“…Even though purely speculative at this point, the suggestion of such ionophoric activity in vesicle membranes is not without biological precedence. Ca-transporting ionophores have been isolated from the membranes of calf heart mitochondria [16,38] and from human kidney tissue [39]. Furthermore, two phospholipids found in matrix vesicle membranes, phosphatidic acid and diphosphatidylglycerol [40], have been shown to possess relatively strong ionophore-like properties in vitro [16,41].…”