1: J Mol Biol  1983 Mar 25;165(1):91-107 

Fluorescence energy transfer studies of transmembrane location of retinal in
purple membrane.

Kouyama T, Kinosita K Jr, Ikegami A.

A diffusion-enhanced energy transfer technique was employed for the
determination of transmembrane location of the retinal chromophore in the purple
membrane. Theoretical considerations showed that the rate of energy transfer
from an energy donor embedded within a membrane to acceptors dissolved in
solvent could be described by an analytical function of the distance a of
closest approach between the donor and acceptor, if the "rapid-diffusion limit"
was attained. The criterion for this limit was given by the relation: (RO)6 much
less than 20D tau Da4, where RO is the characteristic distance of energy
transfer, D is the diffusion coefficient of the acceptor and tau D is the
fluorescence lifetime of the donor in the absence of acceptor. By
photo-reduction of the purple membrane with sodium borohydride, the retinal
chromophore was converted to a highly fluorescent derivative, which showed a
broad emission band in the visible region. From analysis of the fluorescence
decay curves of the photo-reduced purple membrane in the presence of various
concentrations of cobalt-ethylenediamine tetraacetate (Co-EDTA: energy
acceptor), the depth of the chromophore from the membrane surface was estimated
to be 8 (+/-3) A. This result was supported by investigations of energy transfer
processes in a system where the native purple membranes and the photo-reduced
membranes were stacked in parallel: the energy acceptor in this system was the
native retinal chromophore.

PMID: 6405044 [PubMed - indexed for MEDLINE]