METAL ION CHELATORS INHIBIT RETINOL ISOMERIZATION IN BOVINE RPE MICROSOMES

Abstract

Abstract: : Purpose: The isomerization of all–trans–retinol to 11–cis–retinol in RPE is an important but unclear step in the visual cycle. The retinol isomerase was resistant to all attempts to purify it and its activity is unstable during purification. Many features of the isomerase are unknown. This study is aimed to investigate if metal ions are necessary for the isomerase activity. Methods: All–trans [H³]–retinol was used as a substrate to measure LRAT and isomerase activities in bovine microsomes. Metal chelating reagents EDTA and 1,10– phenanthroline were used to study their influence on the reaction. The reaction products were extracted and analyzed by HPLC with a flow scintillation analyzer. Results: The metal ion chelators used in this study decrease the production of 11–cis–retinol from all–trans–retinol. The IC₅₀ was found to be 50 mM for EDTA and 0.5 mM for 1,10–phenanthroline. LRAT activity was not affected by either of these metal ion chelators Conclusion: Our data demonstrate that endogenous metal ion(s) are necessary for the activity of retinol isomerohydrolase.

Keywords: retinoids/retinoid binding proteins • enzymes/enzyme inhibitors • retinal pigment epithelium