INTRAMEMBRANE POSITION OF THE FLUORESCENT TRYPTOPHANYL RESIDUE IN MEMBRANE-BOUND CYTOCHROME-B5

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 dansyl acceptor groups on the surface of the phospholipid bilayer. It was determined that the single fluorescent tryptophanyl residue in vesicle-bound cytochrome b5 and the nonpolar segment is located approximately 20-22 Å below the surface of the bilayer. This position represents a minimum depth of penetration of this portion of the cytochrome in the membrane. © 1979, American Chemical Society. All rights reserved.