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The Effects of Octanol on the Late Photointermediates of Rhodopsin
Author(s) -
Mah Tina L.,
Szundi Istvan,
Lewis James W.,
Jager Stefan,
Kliger David S.
Publication year - 1998
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1998.tb02542.x
Subject(s) - rhodopsin , chemistry , biophysics , biology , biochemistry , retinal
Membrane suspensions of unperturbed rhodopsin and rhodopsin perturbed with 2.5 niM octanol were photo‐lyzed with 477 nm laser pulses at 20 O C and 35°C. Changes in absorbance were monitored at times ranging from 1 u‐s to 80 ms after excitation. The data were analyzed using singular value decomposition, global exponential fitting and kinetic modeling. A recently proposed model involving the photointermediate Meta‐I 380 (T. E. Thorgeirsson, J. W. Lewis, S. E. Wallace‐Williams, and D. S. Kliger, Biochemistry 32,13861–13872, 1993) fits data for samples with and without octanol. Comparison of the microscopic rates shows this alcohol accelerates the formation of Meta‐II via Meta‐I 380 . Activation and equilibrium thermodynamic parameters obtained from Ar‐rhenius plots suggest that octanol reduces the entropy increase in forming both Meta‐I 3g0 and Meta‐II. It also lowers the enthalpy of Meta‐1, SI , relative to Lumi and of Meta‐II relative to Meta‐I 480 . To help determine whether octanol affects the protein directly or indirectly through the lipid bilayer, similar experiments were conducted using rhodopsin solubilized in 0.13% dodecyl maltoside with and without octanol. Spectral shifts in the presence of octanol suggest that a direct protein interaction exists in addition to previously reported effects dependent on membrane free volume.