Identification of cholesterol in the receptor site for rickettsiae on sheep erythrocyte membranes

Cholesterol was identified as an essential component of the receptor on the sheep erythrocyte to which Rickettsia prowazeki adsorbs before lysing the cell. Erythrocytes or ghosts, derived by hypotonic lysis, were treated with proteolytic enzymes, sialidase, sulfhydryl reagents, and periodate without affecting their ability to adsorb rickettsiae. Lipid extracts of ghosts and erythrocytes, on the other hand, contained receptor activity. Fractionation of the lipid extracts by silicic acid column chromatogrphy resulted in the isolation of receptor activity in a neutral lipid fraction. The lipid fractions demonstrated receptor acitity at 34 C but not at 0 C. These properties are also characteristic of the receptor activity with erythrocytes and ghosts. Cholesterol, co-lyophilized with palmitic acid, was found to possess receptor activity. Palmitic acid alone, cholesterol-lecithin, cholestane-palmitic acid, and various phospholipids and glycolipids had no receptor activity. Ghosts treated with amphotericin B or digitonin, compounds that bind to cholesterol in the membrane, lost their ability to adsorb rickettsiae.