Pore-forming action of mastoparan peptides on liposomes: a quantitative analysis.

We have investigated the wasp venom peptides mastoparan X and polistes mastoparan regarding their apparent potential to induce pore-like defects in phosphatidylcholine unilamellar vesicles. Based on a fundamental theoretical model, the pore activation and deactivation kinetics have been evaluated from the observed efflux of liposome entrapped carboxyfluorescein in relation to the bound peptide to lipid ratio. We can quantitatively describe our experimental data very well in terms of a specific reaction scheme resulting in only a few short-lived pores. They evidently emerge rapidly from a prepore nucleus being produced by two rate-limiting monomeric states of bound peptide. These peculiar states would be favorably populated in an early stage of bilayer perturbation, but tend to die out in the course of a peptide/lipid restabilization process.