The Regulation of Vitamin D Metabolism

摘要: It is now firmly established that vitamin D3 (cholecalciferol) must first be converted to more active forms by a series of hydroxylations before exerting its characteristic effects on calcium metabolism. The hydroxylation takes place predominantly in the liver where cholecalciferol 25-hydroxycholecal-ciferol (25 OH D3), major circulating form (l). A second only kidney; 25 hydroxylated mitochondrial enzyme system either position I 1,25 dihydroxycholecalciferol (1,25(OH)2D3) (2), most metabolite known. An alternative step hydroxylates 24 produce 24,25 (24,25 (OH)2D3), less (3).