title: Membrane damage by Cerebratulus lacteus cytolysin A-III. Effects of monovalent and divalent cations on A-III hemolytic activity.
abstract: The effects of monovalent and divalent cations on the hemolytic activity of Cerebratulus lacteus toxin A-III were studied. The activity of cytolysin A-III is remarkably increased in isotonic, low ionic strength buffer, the HC50 (the toxin concentration yielding 50% lysis of a 1% suspension of erythrocytes after 45 min at 37 degrees C) being shifted from 2 micrograms per ml in Tris or phosphate-buffered saline to 20-30 ng per ml in sucrose or mannitol buffered with Hepes, corresponding to a 50-100-fold increase in potency. On the contrary, hemolytic activity decreases progressively as the monovalent cation concentration in the medium increases for Na+, K+, or choline salts. The divalent cations Ca2+ and Zn2+ likewise inhibit the cytolysin A-III activity, but more strongly than do the monovalent cations specified above. Zn2+ at a concentration of 0.3 mM totally abolishes both toxin A-III-dependent hemolysis of human erythrocytes and toxin-induced leakage from liposomes. The observation of similar effects in both natural membranes and artificial bilayers suggests an effect of Zn2+ on the toxin A-III-induced membrane lesion, especially since Zn2+ does not alter binding of the cytolysin. The dose-response curve for toxin A-III exhibits positive cooperativity, with a Hill coefficient of 2 to 3. However, analysis of toxin molecular weight by analytical ultracentrifugation reveals no tendency to aggregate at protein concentrations up to 2 mg per ml. These data are consistent with a post-binding aggregational step which may be affected by the ionic strength of the medium.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Cincinnati, College of Medicine, OH 45267.
authors.forename: J W
authors.initials: JW
authors.lastname: Liu
authors.forename: K M
authors.initials: KM
authors.lastname: Blumenthal
mesh_terms: D000818:Animals; D002413:Cations, Divalent / Q000494:pharmacology; D002414:Cations, Monovalent / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D003603:Cytotoxins / Q000633:toxicity*; D003902:Detergents / Q000494:pharmacology; D004357:Drug Synergism; D004912:Erythrocytes / Q000187:drug effects; D006461:Hemolysis / Q000187:drug effects*; D006801:Humans; D008387:Marine Toxins / Q000633:toxicity*; D009994:Osmolar Concentration
chemical_list: D002413:Cations, Divalent; D002414:Cations, Monovalent; C026601:Cerebratulus lacteus toxin A-III; D003603:Cytotoxins; D003902:Detergents; D008387:Marine Toxins