Application of the transition state theory to water transport across cell membranes

We have applied the transition state theory of Eyring et al. (The Theory of Rate Processes, McGraw-Hill, 1941) to water transport across cell membranes. We have then evaluated free energy (DeltaF(not equal)), enthalpy (DeltaH(not equal)) and entropy (DeltaS(not equal)) of activation for water permeation across membranes, such as Arbacia eggs, Xenopus oocytes with or without aquaporin water channels, mammalian erythrocytes, aquaporin proteoliposomes, liposomes and collodion membrane. DeltaH(not equal) was found to be correlated with DeltaS(not equal). This is so-called DeltaH(not equal) and DeltaS(not equal) compensation over the ranges of DeltaH(not equal) and DeltaS(not equal) from 2 to 22 kcal/mol and from -26 to 45 e.u., respectively, indicating that low DeltaH(not equal) values correspond to negative DeltaS(not equal). Large positive DeltaS(not equal) and high DeltaH(not equal) values might be accompanied by reversible breakage of secondary bonds in the membrane, presumably in membrane lipid bilayer. Largely negative DeltaS(not equal) and low DeltaH(not equal) values for aquaporin water channels, aquaporin proteoliposomes and porous collodion membrane could be explained by the immobilization of permeating water molecules in the membrane, i.e., the partial loss of rotational and/or translational freedoms of water molecules in water channels. (C) 2001 Elsevier Science B.V. All rights reserved.