This study reports the isolation and partial characterization of a soluble protein with binding specificity for retinol from rat testis cytosol. Cytosol, labeled in vitro by addition of [3H] retinol, was fractionated by ion exchange chromatography on DEAE-Sepharose, gel filtration on Sephadex G-50, and preparative polyacrylamide gel electrophoresis. The resulting cytosol binding protein for retinol had been purified at least 1,700-fold, with a yield of approximately 24%. The binding protein for retinol had a molecular weight of approximately 14,600, was homogeneous on disc gel electrophoresis, and was microheterogeneous on isoelectric focusing, showing two close bands of holoprotein with apparent isoelectric points of 4.8 and 4.9. The properties of rat testis cytosol binding protein for retinol differed from those of serum retinol-binding protein in several ways. The purified testis binding protein showed no immunological reactivity when assayed in the radioimmunoassay for rat serum retinol-binding protein and did not display affinity for serum prealbumin, as determined by affinity chromatography on immobilized human prealbumin. A direct comparison of the absorption and fluorescence spectra of the rat testis cytosol binding protein for retinol with those of human serum retinol-binding protein showed significant differences between the two proteins. The purified cytosol binding protein for retinol had an ultraviolet absorption spectrum characterized by two peaks with maxima at approximately 277 and 345 nm. The fluorescence data suggest that retinol bound to serum retinol-binding protein is present in a more rigid conformation than is retinol bound to the cytosol binding protein.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - 1978|
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology