Metabolism of vitamin D: current status.

摘要: There has been much progress in our understanding of the metabolism vitamin D. It is now clear that D3 can be produced skin or ingested diet. accumulates very rapidly liver where it undergoes 25-hydroxylation, yielding 25-OH-D3, major circulating metabolite vitamin. 25-OH-D3 proceeds to kidney one two hydroxylations. If there a biological need for calcium phosphate stimulated convert 1,25-(OH)2-D3, and mobilizing hormone. If, however, animal sufficient supplies phosphate, l-hydroxylase shut down instead converted 24,25-(OH)2D3. The role 24,25-(OH)2D3 remains unknown; may an intermediate inactivation-excretion mechanism. 1,25-(OH)2D3 intestine stimulates intestinal transport transport. also bone mobilization probably other effects yet discovered such tissues as muscle. 25-OH-D3-l-hydroxylase, which located exclusively renal mitochondria, shown three component system involving flavoprotein, iron-sulfur protein (renal ferredoxin), cytochrome P-450. This successfully solubilized, components isolated, reconstituted. 24-hydroxylase, not thoroughly studied. necessary appearance 24-hydroxylase; parathyroid hormone represses 24-hydroxylation. possible 24-hydroxylase represents regulated enzyme, so its presence absence determine whether produced. Two metabolic pathways are known, conversion by 1,24,25-(OH)3D3, unknown substance. In latter instance, occurs loss side chain piece, including at least 26 27 carbons. Whether must metabolized further before carries out all functions established. primary excretion route via bile into feces. Urinary appears small magnitude no products have identified positively. Much learned concerning function D metabolites. should therefore, prove fruitful area investigation many years come, especially since 1,25-(OH)2D3, lalpha-OH-D3 effective number disease states.