Kinetics of ionophore‐mediated transport of Pr³⁺ ions through phospholipid membranes using ¹H NMR spectroscopy

Nuclear magnetic resonance studies of cation transport across vesicle bilayer membranes

“…The mechanistic implications of this will be discussed later. Hunt has depicted similar behavior for A-23187-mediated transport (Hunt, 1975 as has Chen for X-537Amediated transport (Chen, 1978).…”

“…14]. Michaelson et al, 1973 'H Bergelson andBystrov, 1975 'H Lau andChan, 1975 'H Hunt, 1975 'H Chan, 1976 'H Lawaczeck et al, 1976 31p 31p Chrzeszczyk et al, 1976 Cushley andForrest, 1977 'H Lee andChan, 1977 'H Lawaczeck et al, 1977 'H O'Brien et al, 1977 'H 3'P Pierce et al, 1978 'H '3C 'H Gerritsen et al, 1979Hunt and Jawaharlal, 1980 'H Hunt, 1980 THE TIME-COURSE OF THE OUTER HEADGROUP RESONANCE The magnitude of the hyperfine shift of the outer resonance depends upon the concentrations of the paramagnetic shift reagent, the lecithin vesicles, and the concentrations of other competitive species. The shape of the curve expressing this dependence (the NMR binding isotherm) depends in turn upon the affinity constant, the limiting hyperfine shift and the limiting stoichiometry (Chrzeszczyk, 1978).'…”

“…As far as mechanistic information is concerned, however, the spectral behavior of the inner headgroup resonance is more revealing and hence of more interest. It is possible to conduct these experiments in such a way that the inner resonances are observed free of overlap with the outer resonances (Hunt, 1975;Pierce et al, 1978;Hunt, 1980 The "All or Nothing" Process Fig. 2 depicts the 3'P-NMR spectrum of small dipalmitoyl-lecithin (DPL) vesicles as the transport of Pr"3 ions from outside to inside is mediated by ultrasonic irradiation.…”

Mechanism and Specificity of Lanthanide Series Cation Transport by Ionophores A23187, 4-BrA23187, and Ionomycin

“…Lanthanide series trivalent cations (Ln 3ϩ ) are bound (Puskin et al, 1975;Albin et al, 1984;Chapman et al, 1990b) and transported (Hunt, 1975;Hunt et al, 1978Hunt et al, , 1982Amellel et al, 1983;Grandjean et al, 1984;Shastri et al, 1987) by A23187, suggesting that additional transporting species and mechanisms may exist, at least for that ionophore. However, in the existing studies, NMR was used to monitor transport, which was seen as a change in phospholipid headgroup signals reflecting changing concentrations of paramagnetic Ln 3ϩ on opposing sides of the membrane.…”

“…Accordingly, the available data are not sufficient to formulate specific mechanisms for Ln 3ϩ transport, and are conflicting in some aspects. As an example, the stoichiometry (ligand:metal) of the transporting species is in doubt; it is placed at 1:1 by Hunt and co-workers (Hunt, 1975;Hunt et al, 1978) and at 2:1 by Shastri et al (1987). In addition, it is not clear how or if electroneutrality is maintained, and there are no data that reveal transport selectivity for Ln 3ϩ , compared to cations that carry a different charge.…”