Isolation of the protein IMCal, a vitamin D-dependent membrane component of the intestinal transport mechanism for calcium.
Regulation of the intestinal absorption of calcium by vitamin D in the rat involves the synthesis or maintenance of specific membrane proteins. A particulate preparation derived from duodenal mucosal homogenates or isolated microvillus membranes contains at least three vitamin D-dependent activities: calcium binding, p-nitrophenylphosphatase, and calcium-dependent ATPase. The membrane calcium-binding activity correlates closely with calcium transport. Solubilization and biochemical purification have led to the separation of the calcium-binding from the enzymatic activities and to the isolation of the calcium-binding protein (CaBP). This membrane protein has an apparent molecular weight of approximately 200,000 in 0.1% Triton X-100 and yields a monomeric subunit of molecular weight 20,500 in sodium dodecyl sulfate. The new protein, named IMCal, is clearly distinguished from the soluble CaBP found in mucosal homogenates and has a higher affinity for calcium than does the soluble protein. The hypothesis is proposed that IMCal is involved in the facilitated entry of calcium into the enterocyte from the lumen of the intestine.
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000302:isolation & purification*; D007413:Intestinal Mucosa / Q000378:metabolism*; D008565:Membrane Proteins / Q000302:isolation & purification; D008970:Molecular Weight; D051381:Rats; D064030:S100 Calcium Binding Protein G / Q000302:isolation & purification*
D002135:Calcium-Binding Proteins; D008565:Membrane Proteins; D064030:S100 Calcium Binding Protein G; D002118:Calcium