Cholesterol distribution between the two halves of the lipid bilayer of human erythrocyte ghost membranes.

The binding of filipin with cholesterol in sealed and unsealed ghosts prepared from human erythrocytes and in right-side-out and inside-out vesicles prepared from ghosts follows second order kinetics (first order in each reactant). The second order rate constant of interaction of filipin with cholesterol, determined by stopped flow measurements of the initial rate, is slower in sealed ghosts than in unsealed ghosts by a factor of 2.0, whereas identical rate constants were obtained with right-side-out and inside-out vesicles. These results suggest that the cholesterol accessible to rapid reaction with filipin is distributed symmetrically between the inner and outer halves of the lipid bilayer of erythrocyte ghost membranes.