Biochemical properties of the 1α, 25-dihydroxyvitamin D3 cytosol receptors from human and chicken intestinal mucosa

Specific cytopldsmic receptors for 1α, 25-dihydroxyvitamin D3 are shown to be present in human intestinal cytosol which are very similar to the analogous 1α, 25-dihydroxyvitamin D3 receptors present in chick intestinal cytosol. Both receptors are 3.5S proteins which aggregate under low ionic strength conditions. They have molecular weights of approximately 60, 000 and Stokes' molecular radii of 33 Å. The equilibrium dissociation constants for the receptors were both 2 X 10‑10 M at 4 C. The association rate constant for the human receptor was found to be 2.5 X 107 M‑1 min‑1 at 0 C, while a value of 0.5 x 107 M‑1 min‑1 was obtained for the chick receptor. The dissociation rate constants at 4 C were 6.4 x 10‑4 min‑1 (human) and 3.6 X 10‑5 min‑1 (chick). In addition, it was found that both receptors possessed reduced cysteine residues near the 1α, 25-dihydroxyvitamin D3-binding site which were critical for receptor- binding activity. The similarities between the human and the chick receptors suggests that homologous mechanisms for 1α, 25-dihydroxyvitamin D3 interactions may be at work in both mammalian and avian intestinal systems. © 1980 by The Endocrine Society.