Characterization of bovine plasma retinol-binding protein and evidence for lack of binding between it and other bovine plasma proteins.
Bovine retinol-retinol-binding protein (RBP) was isolated from serum as a free, uncomplexed protein under experimental conditions in which human, rabbit, and chicken retinol-RBP are present as tight complexes with prealbumin (thyroxine-binding protein). Purified bovine retinol-RBP formed tight complexes with purified human and chicken prealbumin in physiological ionic strength buffers as judged by gel filtration chromatography, hyperchromic effect on the absorption spectrum of retinol-RBP, and changes in the circular dichroism spectrum. Addition of purified human prealbumin to whole bovine serum shifted the elution position of the specific retinol-RBP fluorescence from a gel filtration column, indicating complex formation in the whole bovine serum. It was concluded from this series of experiments that bovine serum lacks a protein with the binding properties of prealbumin and that bovine retinol-RBP has the normal potential binding to human, chicken, and presumably other prealbumins. Bovine retinol-RBP has a molecular weight, amino acid composition, absorption, and fluorescence spectra which are indistinguishable from that of human retinol-RBP, although the magnitude of the optical rotatory strength of the induced circular dichroism signal at 330 nm was 50% larger in the bovine than in the human material (1.65 and 1.1 Debye-Bohr magnetons, respectively). About 12 liters of bovine and human urine were concentrated by pressure dialysis and a search was made for retinol-RBP using gel filtration and ion exchange chromatography. No retinol-RBP was found in either of these species. This suggested that if, indeed, bovine retinol-RBP is filtered through the kidney's glomeruli due to small molecular size (molecular weight 21,000), there are efficient mechanisms of tubular reabsorption.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001665:Binding Sites; D001798:Blood Proteins / Q000378:metabolism*; D002417:Cattle; D002645:Chickens; D006801:Humans; D008297:Male; D011487:Protein Conformation; D011817:Rabbits; D012177:Retinol-Binding Proteins / Q000097:blood*; D054839:Retinol-Binding Proteins, Plasma; D013045:Species Specificity
D000596:Amino Acids; D001798:Blood Proteins; D012177:Retinol-Binding Proteins; D054839:Retinol-Binding Proteins, Plasma