RBP with Retinol and Other Retinoids

Attempts to form an RBP complex with compounds such as phytol and a number of other terpenoids without the cyclohexene ring structure (Goodman and Raz, 1972 Hase et al., 1976) and with cholesterol were not successful. These results suggest that a structural similarity to retinol in the area of the cyclohexene ring may be necessary for binding to RBP. 

These studies with retinoids have provided some information about the structural requirements of the retinol binding site on RBP. No information is, however, available about the amino acid residues in RBP that are involved in the binding site. Acetylation of lysine residues of RBP did not affect its binding of retinol (Heller and Horwitz, 1975). Modification of one of eight tyrosine residues and two of four tryptophan residues of RBP also had no effect on the retinol-RBP interaction (Heller and Horwitz, 1975 Horwitz and Heller, 1974b). The binding site was, however, disrupted by reduction and alkylation of disulfide bonds (Raz et al., 1970). 

The synthesis of a retinoid affinity label for the retinol binding site of RBP has been reported (Gawinowicz and Goodman, 1982). Three radioactive retinoid bromoacetates were synthesized as potential retinoid affinity labels. The H-labeled compounds synthesized were the bromoacetate derivatives of retinol 

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