A thermodynamic analysis of monovalent cation permeation through a K(+)-selective ion channel.
Ionic selectivity characteristics of the K+ channel from the sarcoplasmic reticulum were studied as a function of temperature in order to decompose the profile of Gibbs free energy along the conduction pore into its enthalpic and entropic components. For Li+, Na+, K+, and Rb+, the enthalpy of binding to the channel is close to zero. Activation enthalpies for transferring ions from bulk aqueous solution to the channel's selectivity region are 20-25 kJ/mol for Na+, K+, and Rb+ and substantially higher for Li+ and Cs+. Transfer of Li+ and Na+ to the selectivity region involved large favorable entropies. The results argue that the group IA cations shed about half their waters of hydration in permeating the selectivity region of this channel.
Miller
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C
Graduate Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02254.
Stahl
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N
Barrol
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M
D000818:Animals; D002414:Cations, Monovalent / Q000493:pharmacokinetics*; D066298:In Vitro Techniques; D007700:Kinetics; D015221:Potassium Channels / Q000502:physiology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013696:Temperature; D013816:Thermodynamics
D002414:Cations, Monovalent; D015221:Potassium Channels