[HTML][HTML] Biochemistry of Visual Pigment Regeneration The Friedenwald Lecture

JC Saari - Investigative ophthalmology & visual science, 2000 - tvst.arvojournals.org
JC Saari
Investigative ophthalmology & visual science, 2000tvst.arvojournals.org
Rods bleached in vivo therefore do not regenerate their visual purple from material within
themselves or in the tissues proximal to them, but from the distally placed pigment
epithelium: the pigment epithelium functions in the regeneration of visual purple; it exerts a
regenerative action on the rods. 1Phototransduction and the visual cycle play
complementary roles in vertebrate vision. Phototransduction is initiated by the
photoisomerization of 11-cis-retinal bound to opsin and ultimately results in a change in the …
Rods bleached in vivo therefore do not regenerate their visual purple from material within themselves or in the tissues proximal to them, but from the distally placed pigment epithelium: the pigment epithelium functions in the regeneration of visual purple; it exerts a regenerative action on the rods. 1
Phototransduction and the visual cycle play complementary roles in vertebrate vision. Phototransduction is initiated by the photoisomerization of 11-cis-retinal bound to opsin and ultimately results in a change in the release of neurotransmitter by photoreceptor cells. The visual cycle restores the product of photoisomerization, all-trans-retinal, to the 11-cis configuration and allows the regeneration of bleached visual pigments (Fig. 1). The biochemical mechanism of phototransduction has been extensively studied during the past 2 decades, and as a result, the process serves as the paradigm for understanding G-protein–coupled receptors in general. In contrast, molecular understanding of the visual cycle is poorly developed, and many fundamental questions regarding reactions, enzymes, and control mechanisms remain unanswered. Sequences of cDNAs encoding three visual cycle enzymes have been published 2 3 4; however, molecular information is unavailable for the other three presumed enzymes of the cycle, including retinol isomerase (isomerohydrolase).
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