title: Interactions of diphtheria toxin with lipid vesicles: determinants of ion channel formation.
abstract: Lipid vesicles have been utilized to study the interactions of diphtheria toxin (DT) with membranes. The assay for DT ion channel formation was fluorescence-detected membrane potential depolarization of vesicles in which valinomycin-induced potassium diffusion gradients had been generated. The following requirements for ion channel formation have been identified: (1) acid pH (less than 5); (2) trans-negative membrane potentials (35-fold increase in channel-forming activity from -6 mV to -59 mV); and (3) negatively charged phospholipid headgroups (about 100-fold more activity using vesicles formed from asolectin compared to soybean phosphatidylcholine). Concentration dependence plots of toxin activity showed a linear response with logarithmic slopes of nearly one for each lipid composition. These results show a close parallel to those obtained previously with planar lipid bilayers and thus provide guidelines for conditions which facilitate functional insertion of the toxin into vesicles.
mesh_terms: D000817:Anilino Naphthalenesulfonates; D004058:Diffusion; D004167:Diphtheria Toxin / Q000378:metabolism*; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008081:Liposomes / Q000378:metabolism*; D008564:Membrane Potentials; D010713:Phosphatidylcholines; D010743:Phospholipids; D011188:Potassium / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D000817:Anilino Naphthalenesulfonates; D004167:Diphtheria Toxin; D005456:Fluorescent Dyes; D007473:Ion Channels; D008081:Liposomes; D010713:Phosphatidylcholines; D010743:Phospholipids; D014634:Valinomycin; C027132:1-anilino-8-naphthalenesulfonate; C024990:asolectin; D011188:Potassium