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Biophys J, August 1999, p. 1024-1035, Vol. 77, No. 2
*Department of Ophthalmology, Harvard Medical School, and the Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114 USA; #Department of Chemistry, State University of Leiden, 2300 RA Leiden, The Netherlands; and §Department of Neurobiology, Stanford University School of Medicine, Stanford, California 94305 USA
In visual pigments, opsin proteins regulate the spectral
absorption of a retinal chromophore by mechanisms that change the energy level of the excited electronic state relative to the ground state. We have studied these mechanisms by using photocurrent recording
to measure the spectral sensitivities of individual red rods and red
(long-wavelength-sensitive) and blue (short-wavelength-sensitive) cones
of salamander before and after replacing the native 3-dehydro 11-cis retinal chromophore with retinal analogs:
11-cis retinal, 3-dehydro 9-cis retinal,
9-cis retinal, and 5,6-dihydro 9-cis retinal. The protonated Schiff's bases of analogs with unsaturated bonds in the ring had broader spectra than the same chromophores bound
to opsins. Saturation of the bonds in the ring reduced the spectral
bandwidths of the protonated Schiff's bases and the opsin-bound chromophores and made them similar to each other. This indicates that
torsion of the ring produces spectral broadening and that torsion is
limited by opsin. Saturating the 5,6 double bond in retinal reduced the
perturbation of the chromophore by opsin in red and in blue cones but
not in red rods. Thus an interaction between opsin and the chromophoric
ring shifts the spectral maxima of the red and blue cone pigments, but
not that of the red rod pigment.
Biophys J, August 1999, p. 1024-1035, Vol. 77, No. 2
© 1999 by the Biophysical Society 0006-3495/99/08/1024/12 $2.00
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