Abstract
The complete amino acid sequence of human serum Retinol-binding protein (RBP) including the distribution of its three disulfide bridges, has been determined. The protein consists of 182 amino acid residues, the order of which was determined following the isolation of five CNBr-fragments. Direct amino acid sequence analysis in an automatic liquid phase sequencer provided almost the entire sequences of the five CNBr-fragments. Several sets of enzymatically derived peptides of RBP were also used to elucidate the primary structure. RBP displays significant homology to bovine beta-lactoglobulin, human alpha 1-microglobulin and rat alpha 1-microglobulin. RBP contains an internal homology. Thus, residues 36 to 83 display statistically significant homology with residues 96 to 141.
Highlights
From its site of synthesis in the liver ( 2 8, 3 6, 4 8 ) the Retinol-binding protein (RBP)' carries one molecule of retinol ( 2 0, 3 3, 3 4 ) to vitamin A requiring cells
While transporting retinol in plasma, RBP forms a stable complex with thyroxine-binding prealbumin ( 2 0, 3 3 )
Cells requiring vitamin A express a receptor for RBP on their cell membranes
Summary
From its site of synthesis in the liver ( 2 8 , 3 6 , 4 8 ) the Retinol-binding protein (RBP)' carries one molecule of retinol ( 2 0 , 3 3 , 3 4 ) to vitamin A requiring cells. While transporting retinol in plasma, RBP forms a stable complex with thyroxine-binding prealbumin ( 2 0 , 3 3 ). This complex formation prevents RBP, which has a molecular weight of 21 000, to pass the kidney glomeruli ( 3 4 ). Cells requiring vitamin A express a receptor for RBP on their cell membranes RBP undergoes a conformational change, the nature of which is presently unknown. This conformational change does not allow a sustained binding between RBP and prealbumin Due to the abolished protein-protein interaction the free RBP molecule becomes degraded in the 'Abbreviations used are: RBP
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