Isomerization activity is inhibited by the iron chelator 2,2-DP. Extracts of 293-F cell cultures transfected with pVitro2/RPE65+CRALBP and pVitro3/LRAT+RDH5 vectors were treated with 2.5 μM all-trans-retinol for 3.5 h in the presence of 0-2,000 μM 2,2-DP. Retinoids were extracted, saponified, and analyzed by HPLC. Values for 11-cis-retinol synthesis in the presence of chelator are normalized to activity in the presence of ethanol vehicle alone, taken as 100% activity. Results are means and SDs of three independent experiments.