Portal copper transport in rats by albumin.

The distribution of newly absorbed copper among serum proteins obtained from the portal circulation of rats was examined by conventional and high-performance gel filtration chromatography, affinity chromatography, and Western blotting. Within 10-30 min after being administered by gavage or directly into the intestine, 67Cu and 64Cu, respectively, were recovered in the albumin fraction. By 8 h after administration of the radionuclides, virtually all of the radioactivity was found with ceruloplasmin. Affigel blue fractionation and subsequent Superose-6 chromatography further demonstrated that all of the copper in the albumin-containing fractions was in fact bound to this protein rather than high molecular weight moieties. Vascular perfusion of the isolated rat intestine, where 64Cu was infused into the lumen, showed that newly absorbed 64Cu in the vascular perfusate collected from the cannulated portal vein was associated with albumin. Uptake of radioactivity by isolated rat liver parenchymal cells from medium containing rat serum with 67Cu bound to albumin was demonstrated. In vitro binding of 64Cu to serum proteins that were transferred to nitrocellulose by Western blotting techniques showed that albumin is essentially the only protein that binds appreciable amounts of copper. The data suggest that albumin is the plasma protein that is responsible for the initial transport of copper after absorption.