Figure 2: Stereospecific requirement of cholesterol in the function of the receptor. (a) Chemical structures of cholesterol and its stereoisomers: ent-cholesterol (enantiomer) and epi-cholesterol (diastereomer). ent-Cholesterol is a nonsuperimposable mirror image of cholesterol, whereas epi-cholesterol is not. (b) The effect of replenishment of cholesterol (chol), epi-cholesterol (epi), and ent-cholesterol (ent) into solubilized membranes (SM) on specific binding of the agonist [3H]8-OH-DPAT to the receptor. Values are normalized to specific binding obtained in native hippocampal membranes (HM). The results show that the requirement of membrane cholesterol for the receptor function is diastereospecific but not enantiospecific. Adapted and modified from [35]. See text for more details.