Lysozyme interactions with phospholipid vesicles: relationships with fusion and release of aqueous content.

We have previously demonstrated that lysozyme induced fusion of negatively charged phospholipid vesicles and have stressed the importance of electrostatic interactions (Posse, E. et al. (1990) Biochim. Biophys. Acta 1024, 390-394). Using centrifugation and fluorescence polarization techniques, we show, in the present paper that lysozyme interacts with negatively charged liposomes (PC/PA, 9:1), but also with neutral liposomes (pure PC). Moreover, the ionic strength and pH of the media did not modify the protein-liposomes interactions. Such interactions induce the spontaneous release of encapsulated Tb-DPA complex in liposomes. Release and fusion of PC/PA liposomes were observed. As indicated by kinetic studies and substrate curves, fusion and release are two uncoupled processes. Taking these and previous results into account we suggest a hypothetical mechanism where a relationship between aggregation, leakage and fusion of liposomes induced by lysozyme interaction is established.