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Activity of cone
visual pigments regenerated with 9-desmethylretinal
Crouch, R1,
Kono, M1, Oprian, D2,
Das, J1 and Corson, D1
Medical University of South Carolina, Charleson SC 294251
Brandeis University, Waltham MA 02454 2
Abstract-
The retinal analogue, 9-desmethylretinal, has a methyl group deleted
on the polyene side chain. This analogue has been shown to form a pigment
with rod opsin, but the loss of the methyl group has a dramatic effect
on the activity and spectral sensitivity of that pigment, causing a
dramatic blue shift in photosensitivity, reducing the quantal response,
and prolonging the response. This has led to the suggestion that this
9-methyl group acts as a "trigger"
in opsins (Shieh et al., J. Mol. Bio., 275,19713, 2000). The purpose
of these experiments was to test this hypothesis in cones. We have expressed
the three salamander cone opsins as well as the rod opsin and regenerated
pigments from these four opsins with 11-cis 9-desmethylretinal. The
rod opsin pigment had similar properties to the previously studied bovine
pigment. All three regenerated cone pigments showed blue shifted absorption
spectra and a sensitivity to hydroxylamine. In transducin activation
assays using bovine rod transducin, the cone pigments were not impeded
in their ability to activate the transducin, unlike the red rod pigment.
Thus in the in vitro experiments, the 9-methyl group does not appear
to be critical for the activity of those opsins. Confirming these data
are the results from suction electrode recordings on the inner segments
of intact salamander red cones. The analogue restored dark adapted flash
to the bleached cones. However, unlike in red rods, the response kinetics
were not slowed. From these experiments we conclude that the 9-methyl
group of retinal does not have the critical role in activation of cones
opsins that it does in the red rod opsin. Supported by NIH EY04939,
Foundation Fighting Blindness and Research to Prevent Blindness.
Keywords: rhodopsin,
retinal, vision, photoreceptor
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