Low affinity of the receptor for 1α, 25-dihydroxyvitamin D₃ in the marmoset, a new world monkey

Circulating levels of 1,25-dihydroxyvitamin D are 10-fold higher in the marmoset, a New World monkey, than in man; to assess hormone receptors, we evaluated interactions of 1,25-dihydroxy vitamin D₃ with virus-transformed lympocytes. soluble extracts of transformed lymphocytes from humans showed hormone binding with affinity and capacity similar to that of receptors for 1,25-dihydroxyvitamin D from other human tissues. However, soluble extracts of transformed lymphocytes from the marmoset showed a strikingly lower affinity for 1,25-dihydroxyvitamin D (K_d 2.2 vs 0.27 nM in marmoset vs human) and a mildly lower binding capacity (6.9 vs 16 fmol mg protein). A defective receptor for 1,25-dihydroxyvitamin D₃ could account for resistance of target tissues to this hormone in the marmoset.