PMID: 7539500Feb 1, 1995Paper

Ion binding constants for gramicidin A obtained from water permeability measurements

The Journal of Membrane Biology
K W WangS B Hladky

Abstract

Gramicidin A pores are permeable to water and small monovalent cations. For K, Rb, and Cs there is good evidence from conductances and permeability ratios that a second ion can enter a pore already occupied by another, but for Na this evidence is inconclusive and comparison of tracer fluxes and single channel conductances suggests that second ion entries are prohibited. Partly as a result of the complications of second ion entry there have been widely differing estimates for the dissociation constants for the first ion in the channel. Dani and Levitt (1981, Biophys. J. 35: 485-499) introduced a method for calculating ion binding constants from simultaneous measurements of water fluxes and membrane conductance. They found no evidence for second ion binding and calculated dissociation constants of 115 mM for Li, 69 mM for K, and 2 mM for Tl. It is shown here that the two-ion, four-state model predicts a dependence of water permeability on ion concentration that is difficult to distinguish from the predictions of block by a single ion. Using a modified technique that allows measurement of higher conductances, the first ion dissociation constants have been determined as 80 mM for Na, 40 mM for Rb and 15 mM for Cs. These values and ...Continue Reading

Citations

Apr 25, 2000·Biophysical Journal·P Pohl, S M Saparov
May 23, 2002·Biophysical Journal·Bert L de GrootHelmut Grubmüller
Oct 9, 1998·The Journal of Biological Chemistry·D M CooperR F Irvine
Jul 10, 2019·Langmuir : the ACS Journal of Surfaces and Colloids·Eric E RossTaylor Johnston

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