[PDF][PDF] Isomerization and oxidation of vitamin a in cone-dominant retinas: a novel pathway for visual-pigment regeneration in daylight

NL Mata, RA Radu, RS Clemmons, GH Travis - Neuron, 2002 - cell.com
NL Mata, RA Radu, RS Clemmons, GH Travis
Neuron, 2002cell.com
The first step toward light perception is 11-cis to all-trans photoisomerization of the
retinaldehyde chromophore in a rod or cone opsin-pigment molecule. Light sensitivity of the
opsin pigment is restored through a multistep pathway called the visual cycle, which effects
all-trans to 11-cis re-isomerization of the retinoid chromophore. The maximum throughput of
the known visual cycle, however, is too slow to explain sustained photosensitivity in bright
light. Here, we demonstrate three novel enzymatic activities in cone-dominant ground …
Abstract
The first step toward light perception is 11-cis to all-trans photoisomerization of the retinaldehyde chromophore in a rod or cone opsin-pigment molecule. Light sensitivity of the opsin pigment is restored through a multistep pathway called the visual cycle, which effects all-trans to 11-cis re-isomerization of the retinoid chromophore. The maximum throughput of the known visual cycle, however, is too slow to explain sustained photosensitivity in bright light. Here, we demonstrate three novel enzymatic activities in cone-dominant ground-squirrel and chicken retinas: an all-trans-retinol isomerase, an 11-cis-retinyl-ester synthase, and an 11-cis-retinol dehydrogenase. Together these activities comprise a novel pathway that regenerates opsin photopigments at a rate 20-fold faster than the known visual cycle. We suggest that this pathway is responsible for sustained daylight vision in vertebrates.
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