Comparative studies on the biological activities of cardiotoxin, melittin and prymnesin.

The actions of cardiotoxin (CTX), melittin and prymnesin were compared on dog erythrocytes, chicken biventer cervicis muscle, rabbit conjunctiva, acetylcholinesterase, succinate-cytochrome c reductase and turbidity of the rat liver mitochondrial suspension. 1. CTX and melittin were approximately equipotent in the various biological activities, while prymnesin was not. 2. The rate of direct ehmolysis induced by CTX was slow, while that induced by either melittin or prymnesin was fast. 3. Phosphate ions, 10mM Ca++, as well as 1 mM reduced glutathione, considerably inhibited the CTX-induced hemolysis, but only slightly inhibited that induced by melittin or prymnesin. 4. CTX, melittin and prymnesin caused contracture of the chicken biventer cervicis muscle. Prymnesin was much less active in this preparation as compared with its hemolytic potency. The CTX contracture was completely inhibited by high Ca++ (10mM) medium, while the melittin contracture was not. 5. The rate of CTX contracture to reach the peak tension was increased when the concentration of CTX was increased, while the rate of melittin contracture did not change very much as the concentrations varied. 6. All three toxins caused a local irritation of the conjunctival sac of the rabbit eye. 7. Both CTX and melittin inhibited acetylcholinesterase and succinate-cytochrome c reductase activities, and also increased the turbidity of the rat liver mitochondrial suspension, while prymnesin was totally inactive in these respects. It is concluded that the mechanism of actions of these toxins may be different at the molecular level. The role of the detergent properties of these toxins in their biological activities is discussed.