ESR measurements on the effects of ethanol on the lipid and protein conformation in biological membranes.

The effects of ethanol on the conformation of proteins or fluidity of lipids was studied in human erythrocyte ghosts and rat brain synaptosomal membranes. A maleimide nitroxide probe (MAL-6) was coupled to membrane protein, or 5-doxylstearic (5NS) was dissolved in the membrane lipid, and the electron spin resonance (ESR) spectra were recorded in the presence of increasing ethanol concentrations and at different temperatures from 4 degrees to 37 degrees. The lipid probe at all temperatures studied showed an increase in fluidity in the membrane lipid when ethanol was added in concentration over 20 mM. The protein probe however required a high concentration of ethanol (200 mM) to produce an increase in the rigidity of the protein conformation of 4 degrees in both erythrocyte and synaptosomal membranes. A decrease in protein rigidity was observed at high ethanol concentrations at 37 degrees only in the erythrocytes. Thus an effect of ethanol on the conformation of membrane protein was observed using MAL-6 only at high ethanol concentrations and depended on the membrane used and the temperature of measurement.