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

Abstract

The administration of vitamin D 3 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 "vitamin D" supernatant (in contrast to "rachitic" supernatant) was indicated by a slower rate of diffusion of Ca 45 across a cellophane dialyzing membrane and by a lesser amount of Ca 45 being bound to an ion-exchange resin (Chelex-100) in the presence of vitamin D 3 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 D 3 -enhanced duodenal absorption of Ca 47 in rachitic chicks occurred almost simultaneously with the appearance of the vitamin D 3 -induced factor, and there was good correlation between the concentration of binding factor and the rate of absorption of Ca 47 .