24-Hydroxylation of 1,25-dihydroxyergocalciferol. An unambiguous deactivation process

J Biol Chem. 1986 Jul 15;261(20):9250-6.


1,24,25-Trihydroxyergocalciferol was isolated from bovine kidney homogenates incubated with 1,25-dihydroxyergocalciferol and from chick kidney homogenates incubated with 24,25-dihydroxyergocalciferol. The identity was established by ultraviolet absorbance, sensitivity to periodate, nuclear magnetic resonance, and mass spectrometry. The new metabolite had an affinity equal to 1,24,25-trihydroxycholecalciferol for the bovine-thymus and chick-intestinal 1,25-dihydroxyvitamin D receptor and had an affinity twice that of 1,24,25-trihydroxycholecalciferol for the rat-intestinal receptor. It was 3- and 6-fold less competitive than either 1,25-dihydroxycholecalciferol or 1,24,25-trihydroxycholecalciferol, respectively, for the rat plasma vitamin D transport protein. 1,24,25-Trihydroxyergocalciferol was at least 10-fold less active than 1,25-dihydroxycholecalciferol, 1,25-dihydroxyergocalciferol, and 1,24,25-trihydroxycholecalciferol at stimulating intestinal-calcium transport and was also relatively ineffective at stimulating bone-calcium resorption in rats. Moreover, in rats, [3H]1,24,25-trihydroxyergocalciferol was cleared from plasma approximately 40% faster than [3H]1,24,25-trihydroxycholecalciferol. These data suggest that C-24 hydroxylation of 1,25-dihydroxyergocalciferol represents a significant in vivo deactivation step, whereas equivalent deactivation of 1,25-dihydroxycholecalciferol seems to involve metabolic steps subsequent to C-24 hydroxylation (C-24 ketonization). C-24 ketonization of 1,25-trihydroxyergocalciferol would not be anticipated due to the presence of the 24(S)-methyl group. These results reveal further dissimilarities between ergocalciferol and cholecalciferol metabolism in mammals and suggest a mechanism for the lesser tendency of ergocalciferol to cause hypercalcemia relative to cholecalciferol.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding, Competitive
  • Biological Transport
  • Bone and Bones / drug effects
  • Bone and Bones / metabolism
  • Calcium / metabolism
  • Cattle
  • Chickens
  • Ergocalciferols / analogs & derivatives*
  • Ergocalciferols / metabolism
  • Ergocalciferols / pharmacology
  • Hydroxylation
  • Intestinal Mucosa / metabolism
  • Intestines / drug effects
  • Kidney / metabolism
  • Kinetics
  • Male
  • Rats
  • Receptors, Calcitriol
  • Receptors, Steroid / metabolism
  • Thymus Gland / metabolism
  • Vitamin D-Binding Protein / metabolism


  • Ergocalciferols
  • Receptors, Calcitriol
  • Receptors, Steroid
  • Vitamin D-Binding Protein
  • 1,24,25-trihydroxyergocalciferol
  • 1,25-dihydroxyergocalciferol
  • 24,25-dihydroxyvitamin D2
  • Calcium