Isolation and properties of cadmium-binding protein induced in rat small intestine by oral administration of cadmium.

The chromatographic properties and amino acid composition of Cd-binding protein induced in the rat small intestine by oral administration of Cd were examined. When the intestinal mucosal cytosol from rats treated orally with Cd was chromatographed on Sephadex G-75, Cd in the intestinal mucosa was bound 95.5% to protein of molecular weight about 10,000. A DEAE Sephadex A-25 chromatogram of the Cd-binding protein from Sephadex G-75 showed two major and one minor Cd-containing peaks as hepatic and renal metallothionein. The amino acid composition of the two major Cd peaks resembled that of metallothionein from other materials examined. These results indicate that the low-molecular-weight Cd-binding proteins in the small intestinal mucosa meet the criteria for classification as metallothionein, and suggest that induced intestinal Cd-binding protein may be capable of preventing the transport of orally administered Cd from the intestinal mucosa into the other organs.