Interactions of all-trans-retinol and long-chain fatty acids with interphotoreceptor retinoid-binding protein.
Interphotoreceptor retinoid-binding protein (IRBP), a predominant protein in the interphotoreceptor matrix of the retina, has been implicated in transfer of retinoids between retinal pigment epithelium and photoreceptor cells. The interactions of IRBP with all-trans-retinol have been studied by three fluorescence-based methods and by measurements of binding of 3[H]-labeled all-trans-retinol to this protein. It was found that IRBP contains two sites with similar but not identical affinities for all-trans-retinol. The dissociation constant of the all-trans-retinol-IRBP complex at the first site was 0.1 microM, which is about 10-fold lower than previously reported values. The second site had about 2.5-fold lower affinity for all-trans-retinol as compared to the first site. Long-chain fatty acids were found in this study to displace all-trans-retinol from the stronger retinol-binding site on IRBP. Displacement of all-trans-retinol was used to study the interactions of fatty acids with this protein. It was found that docosahexaenoic acid (DHA C22:6n-3), an essential fatty acid which plays an important role in vision, had the highest apparent affinity for the site probed on IRBP of all the fatty acids studied.
Chen
Y
Y
Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853.
Saari
J C
JC
Noy
N
N
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002417:Cattle; D004281:Docosahexaenoic Acids / Q000378:metabolism / Q000494:pharmacology; D005230:Fatty Acids, Nonesterified / Q000378:metabolism* / Q000494:pharmacology; D007536:Isomerism; D007700:Kinetics; D008433:Mathematics; D010786:Photoreceptor Cells / Q000378:metabolism*; D012160:Retina / Q000378:metabolism; D012177:Retinol-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D014316:Tritium; D014801:Vitamin A / Q000378:metabolism*
D005230:Fatty Acids, Nonesterified; D012177:Retinol-Binding Proteins; D014316:Tritium; D014801:Vitamin A; D004281:Docosahexaenoic Acids