Abstract
Isolated rat epidermis possesses a cytosolic 3.5 S receptor-like protein for 1,25-dihydroxyvitamin D3. This 3.5 S binder has a high affinity (Kd = 1.4 .times. 10-10 M) for 1,25-dihydroxyvitamin D3 and is present in low concentrations (31 fmol of binding sites per mg of cytosol protein). Analog competition for receptor binding revealed the following potency order: 1,25-dihydroxyvitamin D3 .mchgt. 25-hydroxyvitamin D3 > 1.alpha.-hydroxyvitamin D3 > 24 (R),25-dihydroxyvitamin D3 .mchgt. vitamin D3. The receptor has a MW of 60,000, has affinity for DNA-cellulose, and aggregates in the presence of low K concentrations. The 1,25-dihydroxyvitamin D3 binder is stabilized by sodium molybdate (10 mM). Addition of phenylmethylsulfonyl fluoride (3 mM) yielded more reproducible receptor preparations. The presence of a 1,25-dihydroxyvitamin D3 binding macromolecule with properties similar to those of the bone and intestinal receptor suggests that skin is an additional target organ for this hormone, which is responsible for plasma phosphate and Ca concentration maintenance.