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Proton and Hydroxide Ion Permeability of Phospholipid Vesicles
Yasuhiko Nozaki and Charles Tanford
Proceedings of the National Academy of Sciences of the United States of America
Vol. 78, No. 7, [Part 2: Biological Sciences] (Jul., 1981), pp. 4324-4328
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/10605
Page Count: 5
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The apparent permeability of H+ through phospholipid bilayers was determined by measuring H+ efflux from large unilamellar phospholipid vesicles with internal space buffered at pH 4. The value obtained is about 10-9 cm/sec at room temperature, five orders of magnitude lower than was recently reported for the combined permeability for H+ and OH- [Nichols, J. W. & Deamer, D. W. (1980) Proc. Natl. Acad. Sci. USA, 77, 2038-2042]. The apparent permeability measured in this way is the sum of contributions from the movement of H+ and of uncharged species (HCl or HNO 3) in equilibrium with anions in the solution. There is evidence that the uncharged species make the dominant contribution and that the permeability coefficient for H+ per se is no larger than 5× 10-12 cm/sec. An attempt to measure OH- permeability by use of vesicles buffered at pH 10 did not give a conclusive result because the vesicle walls appeared to be damaged by exposure to this pH. An apparent permeability coefficient of about 10-7 cm/sec was estimated for undamaged membranes.
Proceedings of the National Academy of Sciences of the United States of America © 1981 National Academy of Sciences