PHYSICS OF IONIC CHANNELS AND OTHER PROTEINS WITH AQUEOUS CAVITIES

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Channels made from the peptide alamethicin have been observed while subjected to the osmotic action of differently sized neutral polymers. It is possible not only to see the degree of penetration of the polymers into the channel from their osmotic action but also to follow the kinetics of motion of small polymers through the ionic channel. These channels are sensitive to the phospholipid of the bilayer into which they are incorporated, in particular there is a strong correlation between the probability of high-conductance states and the tendency of the phospholipid to form non-lamellar structures. Hofmeister effect is shown to apply to transport properties of ionic channels. Chaotropic anions bind to roflamycoin channels for longer times, increase their conductance and induce cationic selectivity according to their position in Hofmeister series. In experiments on hemoglobin oxygenation, it is demonstrated that for weak binding reactions the osmotic contributions to binding can be as significant as the direct contribution from solute binding.