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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | Quazi, Faraz Molday, Robert S. |
| Description | Author Affiliation: Quazi F ( Department of Biochemistry and Molecular Biology, Centre for Macular Research, University of British Columbia, Vancouver, BC, Canada V6T 1Z3.); |
| Abstract | The visual cycle is a series of enzyme-catalyzed reactions which converts all-trans-retinal to 11-cis-retinal for the regeneration of visual pigments in rod and cone photoreceptor cells. Although essential for vision, 11-cis-retinal like all-trans-retinal is highly toxic due to its highly reactive aldehyde group and has to be detoxified by either reduction to retinol or sequestration within retinal-binding proteins. Previous studies have focused on the role of the ATP-binding cassette transporter ABCA4 associated with Stargardt macular degeneration and retinol dehydrogenases (RDH) in the clearance of all-trans-retinal from photoreceptors following photoexcitation. How rod and cone cells prevent the accumulation of 11-cis-retinal in photoreceptor disk membranes in excess of what is required for visual pigment regeneration is not known. Here we show that ABCA4 can transport N-11-cis-retinylidene-phosphatidylethanolamine (PE), the Schiff-base conjugate of 11-cis-retinal and PE, from the lumen to the cytoplasmic leaflet of disk membranes. This transport function together with chemical isomerization to its all-trans isomer and reduction to all-trans-retinol by RDH can prevent the accumulation of excess 11-cis-retinal and its Schiff-base conjugate and the formation of toxic bisretinoid compounds as found in ABCA4-deficient mice and individuals with Stargardt macular degeneration. This segment of the visual cycle in which excess 11-cis-retinal is converted to all-trans-retinol provides a rationale for the unusually high content of PE and its long-chain unsaturated docosahexaenoyl group in photoreceptor membranes and adds insight into the molecular mechanisms responsible for Stargardt macular degeneration. |
| ISSN | 00278424 |
| e-ISSN | 10916490 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Issue Number | 13 |
| Volume Number | 111 |
| Language | English |
| Publisher | National Academy of Sciences |
| Publisher Date | 2014-04-01 |
| Publisher Place | United States |
| Access Restriction | Open |
| Subject Keyword | ATP-Binding Cassette Transporters Metabolism Cytoprotection Drug Effects Photoreceptor Cells, Vertebrate Cytology Vitamin A Chemistry Toxicity Adenosine Triphosphate Animals Biological Transport Isomerism Mice Models, Biological Phosphatidylcholines Phosphatidylethanolamines Proteolipids Retinoids Rod Cell Outer Segment Sus Scrofa Research Support, N.I.H., Extramural Research Support, Non-U.S. Gov't Multidisciplinary |
| Content Type | Text |
| Resource Type | Article |
| Subject | Multidisciplinary |
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