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BX Wu, Y Chen, RK Crouch, JX Ma; Identification and Characterization of a Novel All-trans-retinol Short-chain Dehydrogenase in the RPE . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4572.
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Purpose:Retinoid metabolism is essential for the visual cycle, the regulation of gene expression and the development of the retina. The aim of this study is to characterize the novel retinol dehydrogenase, namely RDH9, found predominately in the retinal pigment epithelium (RPE). Methods:A partial cDNA sequence was identified by searching the expressed sequence tag (EST) database. RT-PCR and RACE were used to obtain the full-length cDNA sequences from human retina cDNAs, a bovine RPE cDNA library and mouse eyecup cDNAs. Northern blot analysis and real-time RT-PCR were used to detect the tissue distribution of RDH9. A full-length coding region of human RDH9 was cloned into an expression vector and transfected into COS cells. Retinol dehydrogenase activity was measured in the RDH9-transfected cells and in cell lysates. Results:Novel RDH9 cDNAs containing the complete coding region were cloned from the human, cow and mouse. Each encodes a protein of 341 amino acids, containing a hydrophobic transmembrane helix at its N-terminus. The human, mouse and bovine RDH9 cDNA sequences have 90% homology at the nucleic acid level. The human RDH9 shows 100% and 98.8% identity with bovine and mouse RDH9 at the amino acid level, respectively. RDH9 shares significant sequence homology (34-52%) with other retinol dehydrogenases in the SDR family. RDH9 is predominantly expressed in the RPE, suggesting its role in visual cycle. The activity as measured in RDH9-transfected cells was found to be specific for oxidation of all-trans-retinol to all-trans-retinal. Conclusion:The novel RDH9 is a highly conserved all-trans-retinol dehydrogenase belonging to the short-chain dehydrogenase/reductase (SDR) superfamily. RDH9 may play important roles in the visual cycle.
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