Calcium-ion-binding activity in human small-intestinal mucosal cytosol. Purification of two proteins and interrelationship of calcium-binding fractions.
Ca2+-binding activity was investigated in human small-intestinal mucosal cytosol. Binding was detected in fractions with molecular weights of 28000 and about 900000, as determined by gel filtration. No binding was found at molecular weight 12000-13000 (the molecular weight of calcium-binding protein in lower mammalian species) until the cytosol had been subjected to a hollow-fibre-filtration step. The appearance of Ca2+-binding at molecular weight 12000-13000 was associated with a decline in the 28000-mol.wt. calcium-binding fraction. The 12000-13000-mol.wt. fraction contained two distinct calcium-binding proteins. One of these proteins had properties similar to those of pig calcium-binding protein. Antiserum to this protein reacted against the 28000-mol.wt calcium-binding fraction in cytosol from human small-intestinal mucosa and from human kidney. An immunoassay method for one of the calcium-binding proteins was established. In normal duodenal mucosa the concentration was 915 micrograms/g and in the ileum it was 443 micrograms/g of mucosa. A subject with hypercalcaemic sarcoidosis had 1200 micrograms/g of mucosa in the jejunum, and a subject with an undetectable concentration of plasma 25-hydroxycholecalciferol had concentrations of calcium-binding protein in the mucosa similar to those found in normal subjects.
D000293:Adolescent; D000328:Adult; D000368:Aged; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D003600:Cytosol / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D007118:Immunoassay; D007413:Intestinal Mucosa / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D008970:Molecular Weight
D002135:Calcium-Binding Proteins; D002118:Calcium