Biophys J, November 2000, p. 2526-2534, Vol. 79, No. 5

Desformylgramicidin: A Model Channel with an Extremely High Water Permeability

Sapar M. Saparov,^* Yuri N. Antonenko, Roger E. Koeppe II, and Peter Pohl^*

 ^*Martin-Luther-Universität, Medizinische Fakultät, Institut für Medizinische Physik und Biophysik, 06097 Halle, Germany,  A.N.Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia,  Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA

The water conductivity of desformylgramicidin exceeds the permeability of gramicidin A by two orders of magnitude. With respect to its single channel hydraulic permeability coefficient of 1.1·10¹² cm³ s¹, desformylgramicidin may serve as a model for extremely permeable aquaporin water channel proteins (AQP4 and AQPZ). This osmotic permeability exceeds the conductivity that is predicted by the theory of single-file transport. It was derived from the concentration distributions of both pore-impermeable and -permeable cations that were simultaneously measured by double barreled microelectrodes in the immediate vicinity of a planar bilayer. From solvent drag experiments, approximately five water molecules were found to be transported by a single-file process along with one ion through the channel. The single channel proton, potassium, and sodium conductivities were determined to be equal to 17 pS (pH 2.5), 7 and 3 pS, respectively. Under any conditions, the desformyl-channel remains at least 10 times longer in its open state than gramicidin A.

Biophys J, November 2000, p. 2526-2534, Vol. 79, No. 5
© 2000 by the Biophysical Society   0006-3495/00/11/2526/09  $2.00

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