Effects of preparation method on reversible conformational changes induced by neutral salts in spin-labeled erythrocyte membranes

Addition of “chaotropic” neutral salts to spin-labeled erythrocyte membranes produced changes in membrane conformation proportional to the known activities of the salts: KSCN > CaCl 2 ≥ KNO 3 ⪢ NaCl. The effects had a threshold of about 0.10 m and increased through 0.60 m for all salts. Above 0.6 m other changes due to dielectric effects and/or protein loss began. The chaotropic effects were reversible on removal of the chaotropic ion, for human (or bovine) membranes prepared with a buffer ionic strength of 0.02. For membranes prepared with a buffer ionic strength of 0.005 the changes were irreversible. Exposure to salt concentration greater than 1 m also produced irreversible changes, probably due to solubilization. The results appear to show that the water-soluble membrane proteins are essential to maintain the “native” membrane conformation.