ISOLATION AND CHARACTERIZATION OF A 25-HYDROXYVITAMIN-D BINDING-PROTEIN FROM RAT ENTEROCYTE CYTOSOL

In this study, we have purified and partially characterized a unique p rotein in rat enterocyte cytosol that is capable of binding 25-hydroxy vitamin D-3. The protein was purified using ammonium sulfate precipita tion and gel permeation chromatography, followed by two anion exchange chromatography steps. The protein has an apparent molecular weight of 68,000 assessed by gel permeation chromatography and 58,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Amino acid compos ition and N-terminal amino acid sequence were determined Differences i n chromatographic behavior, molecular weight, amino acid composition, and sequence suggest that the protein is distinct from serum vitamin D binding protein and serum albumin. It differs from the 1,25-dihydroxy vitamin D receptor as well, in its stability during chromatography, cy tosolic location, molecular weight, and sequence and differs from the putative basal-lateral membrane receptor in its cytosolic location. Th e protein isolated is a candidate cytosolic vitamin D-binding protein which may be involved in absorption or in intracellular metabolism of vitamin D metabolites. (C) Elsevier Science Inc. 1997.