Sélectivité du transport de Ca²⁺/Mg²⁺ à travers une membrane liquide par A_•23187 (calcimycine) et son dérivé N-méthyle

Abstract

Operating in a cell of water/CHCl3/water, it is shown that there is a preferential transport of Ca2+/Mg2+ by A.23187. On the basis of measurements of flux of extraction and of flux of liberation in a half-cell of water/CHCl3, it is shown that the selectivity of the transport is related to the kinetics of liberation, which is markedly different for the two ions and which could be explained by the structure of the complex dimers that are formed, according to the corresponding crystallographic studies. The methylation of the —NHCH3 entails an inversion of the selectivity in the transport

Evidence for Dimer Participation and Evidence Against Channel Mechanism in A23187-Mediated Monovalent Metal Ion Transport Across Phospholipid Vesicular Membrane

“…Grell and co-workers (Krause et al, 1983, Grell et al, 1984 have noted a correlation between the relative magnitudes of dissociation rate constants of the Ca 2ϩ and Mg 2ϩ complexes of CAL (determined from stopped-flow and T-jump relaxation studies in methanol and 30% watermethanol mixtures) and the turnover numbers for CALmediated Ca 2ϩ and Mg 2ϩ transports (Pfeiffer et al, 1978). In the "two phase extraction kinetic studies," Jeminet and co-workers (Bolte et al, 1985;Prudhomme et al, 1986) have observed large Ca 2ϩ /Mg 2ϩ selectivity in the rate of release of DM 2ϩ into the aqueous phase by the dissociation of Cal 2 -DM dissolved in the organic phase. Similar observations have been made even when calcimycin analogs were used.…”