Effect of heavy water on the permeability of bilayer phospholipid membranes modified by poly-amino acids

The influence of heavy water on the stationary conductivity (g0) of bilayer phospholipid membranes modified by poly-L-histidine, poly-L-ornithine and poly-L-glutamic acid is studied. The conductivity curves on the plot of conductivity versus pH in heavy water are displaced to the alkaline region due to the isotope effect in ionisation constants of amino acids. The relaxation time (t0) of g0 in D2O is twice greater than in H2O. The registered decrease in g0 values and increase in t0 in heavy water is explained by the strengthening of the hydrated water structure and hydrophobic interactions which lead to the strengthening of the lipid membrane structure and its modified regions. The literature data about isotope effect of the giant squid axon kinetic constants are analyzed. The isotope effects of kinetic ion channel characteristics are interpreted in terms of the proton transition in the proton-transfer complexes. (author)