Colloquium
Recycling of the chromophore of the light-sensitive pigment of vertebrate photoreceptors
Dr. Yiannis Koutalos
Departments of Ophthalmology and Neurosciences
Medical University of South Carolina
Thursday, October 23,
2008, 12:15
p.m.,
SCIC 126
The
recovery of visual sensitivity after exposure to bright light takes
considerable time. This time is used for the regeneration of the
light-sensitive pigment of the photoreceptor cells, a large portion of
which has been destroyed by the exposure to bright light. The
light-sensitive pigment contains an 11-cis retinyl chromophore.
Detection of light involves the photoisomerization of this chromophore
from 11-cis to all-trans, a conversion that also destroys the pigment.
The all-trans chromophore is then recycled to remake the 11-cis isomer,
which is used to regenerate the light-sensitive pigment. The
first reactions of the recycling pathway take place within the
photoreceptor cell. They begin with the release of all-trans
retinal chromophore from the pigment, and its reduction to all-trans
retinol. All-trans retinol is then transported to the adjacent
pigment epithelial cells where it is used to make 11-cis retinal, which
is necessary for the regeneration. We have used the fluorescence of
all-trans retinol to study its formation and removal in isolated living
photoreceptors with real timefluorescence imaging.
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