Fig. 5. A, effects of various RA analogues on the binding of [3H]RA to the M6P/IGF2R. FBS proteins (100 µg) were incubated with [3H]RA (2 µM) in the absence (Cont.) or the presence of 25-fold molar excesses (50 µM) of unlabeled all-trans-RA (RA), retinol (ROH), or retinol acetate (ROHA). The samples were photolyzed and then processed for SDS/PAGE and fluorography. Both retinol and retinol acetate were able to compete with [3H]RA to bind to the IGF2R. B, competitive binding of RA and synthetic retinoids to the M6P/IGF2R. Partially purified M6P/IGF2R from neonatal rat serum was incubated with [3H]all-trans-RA (2 µM) in the absence (Cont.) or the presence of 25-fold molar excesses (50 µM) of unlabeled all-trans-RA (RA), a RAR agonist (TTNPB), or a RAR antagonist (AGN193109). The samples were photolyzed and then processed for SDS/PAGE and fluorography. Both TTNPB and AGN193109 were unable to compete with RA to bind to the IGF2R.