Desformylgramicidin: a model channel with an extremely high water permeability.
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 1.1.10(-12) cm(3) s(-1), 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.
Saparov
S M
SM
Martin-Luther-Universität, Medizinische Fakultät, Institut für Medizinische Physik und Biophysik, 06097 Halle, Germany.
Antonenko
Y N
YN
Koeppe
R E
RE
Pohl
P
P
D020346:Aquaporins / Q000737:chemistry / Q000378:metabolism; D055592:Biophysical Phenomena; D001703:Biophysics; D006096:Gramicidin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D066298:In Vitro Techniques; D007473:Ion Channels / Q000737:chemistry* / Q000378:metabolism; D017136:Ion Transport; D008564:Membrane Potentials; D008567:Membranes, Artificial; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D010539:Permeability; D011522:Protons; D014867:Water / Q000378:metabolism
D020346:Aquaporins; D007473:Ion Channels; D008567:Membranes, Artificial; D011522:Protons; D014867:Water; D006096:Gramicidin; C060781:desformylgramicidin