Retinol-binding protein in human serum: conformational changes induced by retinoic acid binding.
Polyacrylamide gel electrophoresis and isoelectrofocusing followed by immunoblotting technique with an anti-human retinol-binding protein (RBP) serum were used to study holo-RBP and apo-RBP in human plasma. Three observations were made the technique allowed for the first time to directly and quantitatively analyse holo- and apo-RBP. Holo-RBP represented 97.86 +/- 0.78% and apo-RBP 1.94 +/- 0.73% of the total RBP. All-trans-retinoic acid (RA) was found to bind to apo-RBP and to significantly modify the tertiary structure of the protein; this raises the question of RBP involvement in the transport of RA. reconstitution of holo-RBP using apo-RBP from delipidized serum was achieved only after its incubation with natural all-trans-retinoids such as retinol, 3-dehydroretinol and retinoic acid but not with synthetic analogs of retinoic acid (13-cis-retinoic acid, TMMP, 13-cis-TMMP, TTNPB). It appears that RBP has a structure specificity for natural retinoids.
D001059:Apoproteins / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007525:Isoelectric Focusing; D011487:Protein Conformation; D012176:Retinoids / Q000378:metabolism; D012177:Retinol-Binding Proteins / Q000378:metabolism; D054839:Retinol-Binding Proteins, Plasma; D014212:Tretinoin / Q000378:metabolism
D001059:Apoproteins; D012176:Retinoids; D012177:Retinol-Binding Proteins; D054839:Retinol-Binding Proteins, Plasma; D014212:Tretinoin