title: Characterization of a novel protein in chick intestine that exhibits calcium-binding activity and regulation by dietary calcium, aluminum and vitamin D.
abstract: The molecular mechanisms stimulated by vitamin D and low calcium diets that promote intestinal calcium absorption are not fully understood. In the present experiments, groups of chicks were subjected to the following treatments known to alter the efficiency of Ca absorption: vitamin D deficiency, repletion of vitamin D-deficient chicks with 1,25-dihydroxycholecalciferol [1,25(OH)2D3], low Ca intakes, and aluminum toxicity. Duodenal mucosal scrapings were obtained and screened for changes in protein composition using SDS-PAGE and size exclusion chromatography. The relative amount of a previously unreported 400-kDa oligomer containing 22-kDa monomeric subunits was found to vary directly with theoretical changes in the efficiency of Ca absorption, i.e., amounts increased with low Ca intakes and repletion with 1,25(OH)2D3, but were decreased by dietary aluminum and vitamin D deficiency. The oligomer was shown to have Ca-binding activity using a 45Ca overlay technique. These properties suggest 1) that the protein is regulated, at least indirectly, by 1,25(OH)2D3; 2) that the protein may play a role in promoting Ca absorption, possibly by binding Ca; and 3) that dietary aluminum interferes with the regulation of this protein, possibly by interfering with the actions of vitamin D in the intestine.
mesh_terms: D000535:Aluminum / Q000494:pharmacology*; D000818:Animals; D002117:Calcitriol / Q000494:pharmacology; D002132:Calcium Radioisotopes; D002136:Calcium, Dietary / Q000493:pharmacokinetics / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D002645:Chickens; D002850:Chromatography, Gel; D004386:Duodenum / Q000737:chemistry*; D004591:Electrophoresis, Polyacrylamide Gel; D007408:Intestinal Absorption; D008297:Male; D008970:Molecular Weight; D011897:Random Allocation; D014807:Vitamin D / Q000494:pharmacology*
chemical_list: D002132:Calcium Radioisotopes; D002136:Calcium, Dietary; D002135:Calcium-Binding Proteins; D014807:Vitamin D; D000535:Aluminum; D002117:Calcitriol