Characterization of a 1,25-dihydroxy-vitamin D sub(3) receptor in FRTL-5 cells. Evidence for an inhibitory effect of 1,25-dihydroxy-vitamin D sub(3) on thyrotropin-induced iodide uptake

When FRTL-5 cell cytosol was incubated with increasing amounts of ( super(3)H)1,25-dihydroxy-vitamin D sub(3) (( super(3)H)1,25-(OH) sub(2)D sub(3)), saturation of specific hormone binding occurred. Scatchard analysis of specific binding of ( super(3)H)1,25-(OH) sub(2)D sub(3) to the macromolecule yielded an apparent K sub(d) value of 0.41 plus or minus 0.08 x 10 super(-10) M and a single maximum binding capacity of 42.8 plus or minus 8.8 fmol/mg protein. Sucrose gradient analysis revealed substantial ( super(3)H)1,25-(OH) sub(2)D sub(3) association with a macromolecule sedimentating slightly faster than ovalbumin (3.7 S). ( super(3)H)1,25-(OH) sub(2)D sub(3) was completely displaced by excess 1,25-(OH) sub(2)D sub(3). The 1,25-(OH) sub(2)D sub(3)-receptor complex bound to DNA cellulose columns in low salt buffer, and eluted as a single peak at 0.15-0.20 M KCl.