We have developed a method to measure the intramembrane position of the fluorescent tryptophanyl residue in whole cytochrome b5 and the nonpolar membrane binding segment when these molecules are bound to phospholipid vesicles [Koppel, D.E., Fleming, P., & Strittmatter, P. (1979) Biochemistry (preceding paper in this issue)]. The method utilizes excitation energy transfer from the donor tryptophanyl residue in the protein to trinitrophenyl or danysl acceptor groups on the surface of the phospholipid bilayer. It was determined that that single fluorescent tryptophanyl residue in vesicle-bound cytochrome b5 and the nonpolar segment is located approximately 20-22 A below the surface of the bilayer. This position represents a minimum depth of penetration of this portion of the cytochrome in the membrane.
The interaction of alamethicin with both unsonicated lecithin multilayers and sonicated bilayer vesicles has been investigated by nuclear magnetic resonance (nmr) spectroscopy and electron microscopy. It is shown that alamethicin is a surface active agent, which interacts primarily
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