Protection of all- trans retinol by full-length Xenopus IRBP. Three μl of an ethanolic solution of all-trans retinol was added to 400 μl of 2.7 μM full-length Xenopus IRBP in PBS. The final concentration of all-trans retinol in solution was 3.2 μM. The degradation of all-trans retinol was monitored by measuring its absorbance at 325 nm as a function of time. For each sample, absorbance measurements were made every 2 min for 72 minutes. Full-length Xenopus IRBP (filled circles) is able to protect all-trans retinol from degradation as compared to a PBS control (unfilled circles).