CHARACTERIZATION OF RECEPTORS FOR 1,25-DIHYDROXYVITAMIN-D3 IN THE HUMAN TESTIS

Specific high affinity receptors for 1,25-dihydroxyvitamin D3 have been demonstrated in the human testes. The mean binding affinity (Kd ± SD) of the receptor for 1,25-dihydroxyvitamin D3 was 1.75 ± 0.32 × 10-10 M but the binding capacity was low (mean Nmax± SD = 0.53 ± 0,18 fmol/mg protein). Binding was time- and temperature-dependent, with a maximum binding achieved after l h at 25°C. Although binding also took place at 4 and 37°C, higher and more rapid binding was found at 25°C. Furthermore, the binding between the ligand and the receptor was specific since only unlabelled 1,25-dihydroxyvitamin d3 competed with the labelled ligand. Binding of 1,25-dihydroxyvitamin D3 was abolished by trypsin and heat. Sucrose density gradient centrifugation revealed a sedimentation coefficient of 3.6S. © 1990.