Demonstration of two different vitamin D-dependent calcium-binding proteins in rat intestinal mucosa

The characteristics and location of rat intestinal proteins with calcium binding properties were reexamined using both a 45Ca-equilibrated Sephadex G-100 column and the chelex 100 method in the assay of 45Ca binding activity. The rat intestinal mucosa was found to have three different proteins with calcium binding properties. Two of these proteins were found to be vitamin D-dependent and were examined in detail. The larger vitamin D-dependent protein, found predominantly in the jejunum and ileum, had a molecular weight of 27,000 and demonstrated low affinity for calcium; the detection of this protein by the chelex 100 assay was very difficult. The smaller vitamin D-dependent protein, which was associated mainly with duodenum and jejunum, had a molecular weight of 12,500, and demonstrated a high affinity for calcium.