Vitamin D 3 -Induced Calcium-Binding Protein in Chick Intestinal Mucosa

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Abstract
The administration of vita-min D3 to rachitic chicks induces in intestinal mucosal tissue the formation or elaboration of a calcium-binding factor which is found in the supernatant of the mucosal homogenate. The enhanced binding of Ca by the "vitanmin D" supernatant (in contrast to "rachitic" supernatant) was indicated by a slower rate of diffusion of Ca45 across a cellophane dialyzing membrane and by a lesser amount of Ca45 being bound to an ion-exchange resin (Chelex-100) in the presence of vitamiiin D3 supernatant. The binding activity was only associated with the protein fraction from a Sephadex G-25 column and was destroyed by trypsin digestion. This and other evidence suggest that the soluble factor is a protein. The vitamin D3-enhanced duodenal absorption of Ca47 in rachitic chicks occurred almost simultaneously with the appearance of the vitamin D3-induced factor, and there was good correlation between the concentration of binding factor and the rate of absorption of Ca47.