1,25-Dihydroxycholecalciferol stimulation of a mitochondrial protein in chick intestinal cells

The steroid hormone 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) stimulates the absorption of dietary calcium by the small intestine of animals although the exact mechanism by which this is achieved remains unclear. However, it has long been known that a soluble, calcium-binding protein (CaBP), is produced in large amounts in the cytoplasm of the intestinal cells of animals after in vivo administration of vitamin D3 or 1,25-(OH)2D3 (refs 1,2). We report here that 1,25-(OH)2D3 administered in vivo to rachitic chickens also stimulates production of another protein with molecular weight (MW) 39,000-42,000 which is insoluble in the absence of detergent, is found in the outer mitochondrial membrane and is produced in advance of maximum calcium transport.