Untransfected cells (solid gray trace) or Tet-induced HEKK-RetSat cells (solid black trace) were homogenized and incubated with all-trans-retinol substrate, followed by retinoid extraction and normal phase HPLC analysis. The elution profile was monitored at 290 nm for the appearance of all-trans-13,14-dihydroretinol. In control samples (short dashed black trace) cell homogenate from HEKK-RetSat cells was boiled 10 min at 95 °C prior to incubation with substrate. The addition of 0.4 mM NADH or NADPH had no effect on the yield of all-trans-13,14-dihydroretinol. The experiment was performed in duplicate. The peak numbers represent 13-cis-retinol (1), all-trans-13,14-dihydroretinol (2), 9,13-di-cis-retinol (3), 9-cis-retinol (4), and all-trans-retinol (5). mAU, milliabsorbance units.