Evidence for nystatin micelles in L-cell membranes from fluorescence photobleaching measurements of diffusion.

Diffusion of a nitrobenzoxadiazole derivative of the polyene antibiotic nystatin in the membranes of L cells is found to depend on the concentration of nystatin in the membrane. Its diffusion coefficient measured by fluorescence photobleaching decreases hyperbolically as the concentration of nystatin is increased. This behavior is reproduced when the concentration of the derivative is increased. In contrast, diffusion of a nitrobenzoxadiazole derivative of a phospholipid is insensitive to the nystatin concentration under these conditions. The nystatin-specific diffusion changes can be understood if nystatin exists in a monomer-micelle equilibrium within the membrane but cannot be accounted for by binding or phase partitioning.