Figure 4. Release of 11-cis- and 9-cis-retinal from CRALBP. A: Cellular retinaldehyde-binding protein (CRALBP)·11-cis-retinal (6 μM) was incubated in the dark with 2 mM NH₂OH and small unilamellar vesicles (SUVs). The total phospholipid concentration was 90 μM, and SUVs were composed of 100 mol% phosphatidylcholine (PC) or 50 mol% PC and 50 mol% other lipids, as indicated. After 16 h at room temperature, retinoids were extracted and quantified by high performance liquid chromatography. The amount of 11-cis-retinal oximes (syn+anti) reflected the release of 11-cis-retinal for reaction with NH₂OH during the incubation. The amount of 11-cis-retinal released from by PC: phosphatidic acid (PA) was approximately 75% of the total bound to CRALBP. The results shown are from a single experiment. B: CRALBP·9-cis-retinal (6 μM) was incubated in the dark with NH₂OH and SUVs as described. Spectra were obtained before and 3 h after addition of the SUVs. The results are shown as the % of the maximum spectral change resulting from incubation with 4 M urea. Error bars shown are standard deviations from the means (n=3). The abbreviations used are: phosphatidic acid (PA); phosphatidylcholine (PC); phosphatidylethanolamine (PE); phosphatidylinositol (PI); phosphatidylserine (PS).