Interaction of 1 alpha, 24-dihydroxyvitamin D3 with the chick intestinal 1 alpha, 25-dihydroxyvitamin D3 receptor system.

The interaction of 1 alpha, 24-dihydroxyvitamin D3 with the 1 alpha, 25-dihydroxyvitamin D3 receptor system was studied in chick intestinal mucosa. The competitive receptor binding assay indicated that 1 alpha, 24-dihydroxyvitamin D3 bound to a cytosol 1 alpha, 25-dihydroxyvitamin D3 receptor with a relatively high affinity compared with other vitamin D3 analogs. The R-isomer of 1 alpha, 24-dihydroxyvitamin D3 revealed higher affinity for the receptor than the S-isomer. In the reconstituted cytosol-chromatin system, bith 1 alpha, 24(R)-dihydroxy[3H]-vitamin D3 and 1 alpha, 24(S)-dihydroxy-[3H]-vitamin D3 specifically associated with chromatin via a temperature-dependent process. The association of 1 alpha, 24-dihydroxy-[3H]-vitamin D3 with chromatin was reduced in the presence of competing unlabeled 1 alpha, 25-dihydroxyvitamin D3. Furthermore, the chromatin-associated 1 alpha, 24-dihydroxy-[3H]-vitamin D3 was dissociated by a high concentration of KCl, likewise 1 alpha, 25-dihydroxy-[3H]-vitamin D3. From these results, it is strongly indicated that 1 alpha, 24-dihydroxyvitaim D3 is recognized by cytosol 1 alpha, 25-dihydroxyvitamin D3 receptor as an analog of 1 alpha, 25-dihydroxyvitamin D3 and associates with chromatin by the same mechanism as 1 alpha, 25-dihydroxyvitamin D3.