Intestinal membrane calcium-binding protein. Vitamin D-dependent membrane component of the intestinal calcium transport mechanism.
A particulate fraction of rat intestinal mucosal homogenates, termed the "calcium-binding complex," contains three vitamin D-dependent activities: calcium binding of high affinity, calcium-dependent adenosine triphosphatase, and p-nitrophenylphosphatase. These particulate activities vary concordantly with intestinal calcium transport, suggesting that they represent membrane components of the translocation mechanism. The particulate was solubilized with 1-butanol and the activities were resolved partially by gel filtration and by DEAE-cellulose and spheroidal hydroxyl-apatite column chromatography. The Ca-binding activity was separated from the enzymes and isolated as a protein of molecular weight approximately 200,000, as estimated by gel filtration in 0.1% Triton X-100. The membrane protein, named IMCal (intestinal membrane calcium-binding protein), was dissociated with sodium dodecyl sulfate to yield a monomer of molecular weight 20,500 which is clearly distinguishable from the soluble calcium-binding protein (molecular weight 11,500) of rat mucosa. The apparent dissociation constants of Ca2+ of IMCal and of the soluble calcium-binding protein were estimated as 0.37 microM and 2.25 microM, respectively. The vitamin D-dependent activities of the calcium-binding complex are present in isolated intestinal microvillus membranes and may mediate the translocation of calcium from the intestinal lumen to the cytosol.
D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D004386:Duodenum / Q000378:metabolism; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D008297:Male; D008970:Molecular Weight; D051381:Rats; D064030:S100 Calcium Binding Protein G / Q000302:isolation & purification / Q000378:metabolism*
D000596:Amino Acids; D002135:Calcium-Binding Proteins; D064030:S100 Calcium Binding Protein G; D009597:4-Nitrophenylphosphatase; D000252:Calcium-Transporting ATPases; D002118:Calcium