Rate limiting step in vitamin D synthesis is?
ANSWER: (B) 1, 25-dihydroxycholecalciferolREF: Ganong 22ed chapter 21, Harrison 17 " edition chapter 21 Vitamin-D: Synthesis and Metabolism1, 25-dihydroxyvitamin D is the major steroid hormone involved in mineral ion homeostasis regulationVitamin D is subsequently 25-hydroxylated in the liver by cytochrome P450-like enzymes in the mitochondria and microsomes. The activity of this hydroxylase is not tightly regulated, and the resultant metabolite, 25-hydroxyvitamin D , is the major circulating and storage form of vitamin DThe second hydroxylation, required for the formation of the mature hormone, occurs in the kidney. The 25-hydroxyvitamin D-l-hydroxylase is a tightly regulated cytochrome P450-like mixed function oxidase expressed in the proximal convoluted tubule cells of the kidney
25 cholecalciferol
1, 25-dihydroxycholecalciferol
24, 25- dihydroxycholecalciferol
7-dehydrocholesterol
Vitamins