Retinol transport system in cattle and purification of retinol-binding protein from bovine serum

Retinol transport system in cattle was investigated, followed by the purification and characterization of bovine serum retinol-binding protein (RBP). Gel filtration of serum from cow produced two retinol peaks, peak 1 and 2. The major, peak 1 having higher molecular weight corresponded to the retinol peak from human serum which consisted of RBP and prealbumin (PA). The peak 2 which was not presented in the human serum had lower molecular weight (about 20,000). In the presence of 3.0 M urea, the peak 1 was almost disappeared and peak 2 was increased. On the other hand, in the serum from calf, major retinol peak was corresponded to the peak 2 from cow. These results suggested that, in cow, retinol was transported by the complex of RBP and another protein, presumably PA, but in calf, mainly by RBP alone. Purification of bovine RBP was carried out by using four chromatographic steps as follows; 1. DEAE-cellulose (pH 6.0), 2. Sephadex G-100 (using the buffer containing 3.0 M urea), 3. DEAE-cellulose (pH 8.3), 4. Sephadex G-100. From 1,100 ml of serum, 14.1 mg of bovine RBP was finally obtained and the overall recovery was estimated to be about 32%. Its molecular weight, ultraviolet absorption and fluorescence spectra, electrophoretic mobility, and amino acid composition were similar to those of other species.