Penetration of phospholipid monolayers by cardiotoxins

The monomolecular film technique was used to compare the specific interaction of four cardiotoxins from Naja mossambica mossambica with different phospholipids. We were able to demonstrate the interaction of cardiotoxins (10(-7) M) with both neutral and negatively charged phospholipids up to very high surface pressures (45 dyn/cm). In the presence of a phospholipid monolayer, the surface activity of cardiotoxins became much greater than that observed at the air-water interface. Neurotoxins of the same venom do not penetrate a phospholipid film, even at low surface pressure (15 dyn/cm). The apparent molecular area of cardiotoxin III during its insertion into a negatively charged phospholipid film was quantitatively defined. As a function of surface pressure of the membrane around 25 dyn/cm, cardiotoxins may exist in two different configurations, "flat" (1400 A2) or "edgewise" (420 A2). This result could account for the lytic activity of this type of toxin.