Vitamin D-Induced Calcium Binding Factor in Rat Intestinal Mucosa.

Abstract

Oral administration of 500 IU of vitamin D2 or vitamin D3 to rachitic rats resulted in the elaboration of a Ca-binding factor which could be detected in the supernatant fraction of duodenal mucosal homogenates at 72 hours after administration of the vitamin. This factor was found to be associated with the initial or protein containing portion of the supernatants after percolation through Sephadex G-25; this indicates that the factor is a macromolecule, presumably a protein. Further separation of the supernatants by Sephadex G-100 gel filtration showed that the increased binding activity seen after vitamin D administration was mainly associated with only one of the protein peaks present in the Sephadex G-100 fractions. This particular peak was much less prominent in the fractionated supernatant of the mucosal homogenates from rachitic rats. The results suggest that the vitamin D-dependent binding activity is due to the presence of a specific calcium binding protein in the supernatant fraction of duodenal mucosal homogenates from vitamin D-treated rachitic rats.