Dielectric relaxation studies of ionic processes in lysolecithin-packaged gramicidin channels

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Abstract
Dielectric permittivities have been determined for suspensions of lysolecithin packaged malonyl gramicidin channels over the frequency range of 5kHz to 900 MHz and under conditions of approximately equimolar concentrations (≈10mM) of channels and salts. The salts were lithium chloride, sodium chloride and thallium acetate. A relaxation process unique to the thallium acetate-channel system was observed which on analysis gave rise to a relaxation time at 250 of 120 nsec. The permittivity data, as well as a comparison of binding constants, indicate that the relaxation process results from Tl+ being bound within the channel and more specifically from an intrachannel ion translocation with a rate constant of approximately 4×106 sec−1 and with an energy of activation of less than 6.7 kcal/mole. These data compare favorably with data from conductance studies on planar bilayers and with ion and carbon-13 nuclear magnetic studies on the lysolecithin packaged malonyl gramicidin channels which combine to indicate that the relaxation process is due to the jump of the thallium ion across a central barrier.

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