title: The 24-hydroxylation of 1,25-dihydroxyvitamin D3.
abstract: The production of 1,24,25-trihydroxyvitamin D3 in vivo in vitamin D-deficient rats has been demonstrated from either 25-hydroxyvitamin D3 or 1,25-dihydroxyvitamin D3. The stereochemical configuration of the hydroxyl on the 24 position of 1,24,25-trihydroxyvitamin D3 has also been unambiguously established to be R. Nephrectomy failed to eliminate the conversion of 1,25-dihydroxyvitamin D3 to the 1,24,25-trihydroxyvitamin D3, establishing that the 24-hydroxylase can be demonstrated in at least one organ in addition to kidney in contrast to the 1-hydroxylase. 1,24,25-Trihydroxyvitamin D3 can also be produced in vivo from 1alpha-hydroxyvitamin D3 or from 24-hydroxyvitamin D3, analogs of vitamin D3 which are not naturally occurring. Using chick kidney mitochondrial preparations it has been demonstrated that the 24-hydroxylase is able to utilize 1,25-dihydroxyvitamin D3 as a substrate whereas it is unable to utilize 1alpha-hydroxyvitamin D3. In addition, the chicke kidney 1-hydroxylase is known to convert 24,25-dihydroxyvitamin D3 to the 1,24,25-trihydroxyvitamin D3, but this hydroxylase is unable to act on the 24-hydroxyvitamin D3. These results demonstrate that the renal vitamin D hydroxylases require that a hydroxyl be on the 25 carbon of the vitamin D molecule before it can be 1- or 24-hydroxylated.
mesh_terms: D000818:Animals; D002645:Chickens; D004100:Dihydroxycholecalciferols / Q000378:metabolism*; D006887:Hydroxycholecalciferols / Q000096:biosynthesis / Q000378:metabolism* / Q000494:pharmacology; D007668:Kidney / Q000187:drug effects / Q000201:enzymology; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology; D009392:Nephrectomy; D051381:Rats; D013250:Steroid Hydroxylases / Q000378:metabolism*; D014808:Vitamin D Deficiency / Q000201:enzymology
chemical_list: D004100:Dihydroxycholecalciferols; D006887:Hydroxycholecalciferols; C013721:1,24,25-trihydroxyvitamin D3; D013250:Steroid Hydroxylases