title: The 1 alpha-hydroxylation of 24-hydroxyvitamin D3 by chick kidney homogenates.
abstract: Tritium-labeled 24(R)-hydroxyvitamin D3 and 24(S)-hydroxyvitamin D3 were chemically synthesized and the 1 alpha-hydroxylation of these compounds by chick kidney homogenates was studied. A marked stereospecific preference with regard to the orientation of the hydroxyl functionality on carbon-24 was noted: while the 24(R)-epimer could be 1 alpha-hydroxylated in readily detectable amounts, the 24(S)-epimer was not hydroxylated. Thus, 1.2 micrograms of 1 alpha,24(R)-dihydroxyvitamin D3 was isolated and its structure confirmed by mass spectrometry. The relative rate of 1 alpha-hydroxylation of 125 nM substrate tritiated 24(R)-hydroxyvitamin D3 and 25-hydroxyvitamin D3 (the presumed natural substrate for the renal 1 alpha-hydroxylase) was 1:6.7.
mesh_terms: D000818:Animals; D002112:Calcifediol / Q000378:metabolism*; D002645:Chickens; D002852:Chromatography, Ion Exchange; D006900:Hydroxylation; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D013058:Mass Spectrometry; D014316:Tritium
chemical_list: D014316:Tritium; D002112:Calcifediol