Four approaches - 1) peptide syntheses, 2) physical characterization of the channel state in bilayer suspensions, 3) planar bilayer studies of channel transport by the same peptides and 4) theoretical analyses of molecular mechanics of channel function - are integrated in a thorough study of channel mechanisms in biomembranes using Gramicidin A, carefully selected analogs and derivatives. The purposes of the analogs and derivatives are: a) to vary side distributions and energetics of peptide libration, b) to vary channel length, c) to introduce negative charge in the cation binding site, and d) to alter the height of the central barrier. The channel states of the peptides will be physically characterized, principally using NMR and dielectric relaxation methods, in terms of ion binding and rate constants and their temperature dependences. In parallel, planar bilayer studies will be carried out to assess the effects a) of varied side chains on distribution of single channel currents, b) of varied channel length on mean channel lifetime and on magnitude of single channel currents, c) of negative charge in the binding site, d) of varying the height of the central barrier, e) of temperature on single channel currents of ions of different radii and with membranes of different viscosity, and f) of temperature on the """"""""on-off"""""""" kinetics in membranes of different viscosity. Theoretical analyses will map distributions of side chains of GA and its analogs, calculate dimerization energetics for selected analogs, treat channel deformation necessary for ion binding, and examine the relationship between side chain orientation and energetics of peptide libration. The purpose of these studies is to understand fundamental factors involved in selective ion transport by the channel mechanism, to provide a model system for developing knowledge of rate processes in condensed media, and to arrive at a unique description of the kinetics of Gramicidin A channel transport. The latter is to be achieved by using independently determined binding, rate and other physical constants to calculate single channel current data obtained from the planar bilayer studies. Fundamental physico-chemical quantities are being obtained in studies of Gramicidin A channel transport. Furthermore, it is generally appreciated that this channel exhibits phenomenology markedly similar to that of physiological channels. Additionally, medical disorders ranging from hypertension, cardiac arrhythmias and depression are being addressed in terms of modification of channel activity.
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