The α-helix to β-sheet transition in poly(l-lysine): Effects of anesthetics and high pressure

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Poly(l-lysine) exists in a random-coil formation at a low pH, α-helix at a pH above 10.6, and transforms into β-sheet when the α-helix polylysine is heated. Each conformation is clearly distinguishable in the amide-I band of the infrared spectrum. The thermotropic α-to-β transition was studied by using differential scanning calorimetry. At pH 10.6, the transition temperature was 43.5°C and the transition enthalpy was 170 cal/mol residue. At pH 11.85, the measurements were 36.7°C and 910 cal/mol residue, respectively. Volatile anesthetics (chloroform, halothane, isoflurane and enflurane) partially transformed α-helix polylysine into β-sheet. The transformation was reversed by the application of hydrostatic pressure in the range of 100–350 atm. Apparently, the α-to-β transition was induced by anesthetics through partial dehydration of the peptide side-chains (β-sheet surface is less hydrated than α-helix). High pressure reserved this process by re-hydrating the peptide. Because the membrane spanning domains of channel and receptor proteins are predominantly in the α-helix conformation, anesthetics may suppress the activity of excitable cells by transforming them into a less than optimal structure for electrogenic ion transport and neurotransmission. Proteins and lipid membranes maintain their structural integrity by interaction with water. That which attenuates the interaction will destabilize the structure. These data suggest that anesthetics alter macromolecular conformations essentially by a solvent effect, thereby destroying the solvation water shell surrounding macromolecules.

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