INTERACTION OF 1α, 24-DIHYDROXYVITAMIN D₃ WITH THE CHICK INTESTINAL 1α, 25-DIHYDROXY VITAMIN D₃ RECEPTOR SYSTEM

Abstract

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