FIGURE 7.

Retb binds riboflavin in vitro. A, immunocytochemistry of Retb-, rbp-, and Enox2-transfected cells at ×60 (upper panels), ×100 (lower panels), secondary only (mock-transfected cells) at ×20 (upper panel), and Dil only at ×20 (lower panel). B, immunoblots of soluble, S-Na2CO₃ and IS-Na₂CO₃ protein extracts from COS-7 cells transfected with FLAG-tagged Retb-, rbp-, Enox2-, or mock-transfected COS-7 cells. Upper blots probed with FLAG antibody, and lower panels probed with Gapdh antibody. C, absorbance of membranes isolated from COS-7 cells incubated in media containing 0.075 mm riboflavin as well as from subsequent separated IS-Na₂CO₃ and S-Na₂CO₃ fractions. Absorbance at 340 nm was divided by the ratio of FLAG to Gapdh signal assessed from immunoblots. Results demonstrate that Retb binds riboflavin at levels comparable with RBP. Scale bar, 10 μm.