ASSOCIATION OF POLYENE ANTIBIOTICS WITH STEROL-FREE LIPID-MEMBRANES .2. HYDROPHOBIC BINDING OF NYSTATIN TO DILAUROYLPHOSPHATIDYLCHOLINE BILAYERS

Interaction of nystatin A(1) with multilamellar vesicles (MLV) of dila uroylphosphatidylcholine (DLPC), observed either by adding nystatin to preformed MLV (mixtures I) or by incorporating it during the formatio n of vesicles (mixtures II, inner lamellas of MLV in contact with nyst atin) was investigated for 0.002 less than or equal to nystatin/DLPC = R-A less than or equal to 0.20, by four complementary methods. The ma in results were: (i) Ultraviolet absorption and circular dichroism (CD ) spectra of mixtures I revealed the occurrence of a saturable associa tion with a stoichiometry (R-A = 0.007 +/- 0.002) constant between 3 a nd 33 degrees C. (ii) By differential scanning calorimetry, thermogram s of the two types of mixtures were similar only when water was in gre at excess. In the opposite (e.g., (H2O)/(DLPC) = R-W less than or equa l to 300), mixture II thermograms displayed two features, upshifted by about 6.5 degrees C with respect to the sharp peak observed with mixt ure I, resembling those obtained for pure DLPC when the low-temperatur e phase was the subgel phase. For this R-W, the nystatin absolute conc entrations were those for which nystatin form superaggregates as revea led by the nystatin CD spectra. It is proposed that these superaggrega tes are excluded from the interlamellar spacings of MLV and exert a pu mping action on the interlamellar water, The subsequent dehydration of the inner lamellas is thought to convert them into the subgel state, (iii) H-2-NMR spectra of sn-2-perdeuterated DLPC MLV + nystatin mixtur es II, confirmed such a temperature shift of the main transition. They showed, in addition, an ordering of the aliphatic chains immediately above the transition temperature, equivalent to a bilayer thickening o f 2 Angstrom.