BINDING OF SODIUM ALKYL SULFATES TO HUMAN ERYTHROCYTE STUDIED WITH A SURFACTANT ION-SELECTIVE ELECTRODE

To clarify the mechanism of the shape change of human erythrocyte indu ced by anionic surfactants, the binding of sodium alkyl sulfates (CnH2 n+1OSO3Na, n = 8, 10, 12) to human erythrocyte was studied. In the bin ding experiments with surfactant ion selective electrodes, it was foun d that all surfactants studied bound to the erythrocyte in two steps i n the concentration range where the shape change occurred. From the an alysis of binding isotherms, the binding constants (K-1, K-2) and the total number of sites (n(1), n(2)) for each binding were obtained. K-1 is larger than K-2 for each surfactant; both K-1 and K-2 increase wit h the number of the carbon atoms of the alkyl group of the surfactants . These facts suggest that the first binding is stronger than the seco nd binding and that the hydrophobic interaction between the alkyl chai n of the surfactants and the erythrocyte is the main driving force for each binding. Meanwhile, from the optical microscopic observation, it was found that the echinocyte was induced only in the concentration r ange of the second binding. Furthermore, to identify the binding sites on the erythrocyte membrane for the surfactants, the differential sca nning calorimetry (DSC) measurements of erythrocyte ghost were done, a nd it was elucidated that the first binding site was the boundary lipi d region of band 3 and the second binding site was the phospholipid la yer of the erythrocyte membrane. These results imply that the shape ch ange of the erythrocyte progresses via two steps of surfactant binding , first, to the membrane protein, band 3, and second, to the lipid lay er of the erythrocyte, and that the membrane proteins also play an imp ortant role in the mechanism of the shape change of the erythrocyte.