Photolabeling of staphylococcal alpha-toxin from within rabbit erythrocyte membranes

Intrinsic membrane proteins of rabbit red blood cells were labeled with the photoreactive amphipatic reagent 12-(4-azido-2-nitrophenoxy) stearoyl (1-14C) glucosamine, which inserts into the hydrophobic membrane region and generates a reactive nitrene upon ultraviolet irradiation. Photolabeling of membrane-bound staphylococcal alpha-toxin after lysis of probe-treated rabbit red blood cells by this toxin implies its penetration into the hydrophobic region of the outer leaflet of the membrane. In contrast clostridial theta-toxin and staphylococcal delta-toxin were not labeled, but extraction of intrinsic membrane proteins by delta-toxin was evidenced.