Portal copper transport in rats by albumin

Abstract

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.

Role of extracellular zinc and copper on metallothionein regulation in cultured rat hepatocytes

“…The MT content of hepatocytes maintained in media supplemented with 1, 10 or 50 p,mol/L Cu, as measured by RIA, was slightly but significantly greater than that shown by hepatocytes maintained without metals in the medium at all times studied. MT levels were in general similar to those shown by hepatocytes maintained with Zn; as for Zn (91, Cu accumulation in the hepatocyte appears to equilibrate by exchange with Cu pools (5), a process where albumin may play an important role (1,8,11,36,39,43). Collectively, these data suggest that in physiological conditions the hepatocyte is equally capable of controlling and maintaining specific intracellular Cu levels, as it does with Zn levels.…”

“…Thus, about two thirds of the Zn and 5% of the Cu is bound to albumin, whereas 90% of the Cu is bound to ceruloplasmin (1). However, a substantially higher percentage of Cu should be bound to albumin in the portal blood because it appears that this protein is responsible for the initial transport of Cu to the liver after absorption by the intestine (36). The same was previously demonstrated for Zn (37,38).…”

Changes in Plasma Copper and Zinc during Rat Development

“…Regarding the binding to plasma compo nents the 4 different elution volumes where copper was found were as previously reported [1,10,11,13], Association of copper to highmolecular-weight proteins has been reported [14,17]; yet the identity of these is still contro versial [18], Nevertheless, the high-molecularweight component would be considered in the labile pool of plasma copper and not to be related to ceruloplasmin [14,17]. Ceruloplas min, which is the main copper-containing protein in the adult plasma [1,10,11], is low in the fetus and especially in the newborn, which is probably related to the lack of ability of its liver to synthesize the protein [5].…”

Separation of Selenium-Containing Proteins in Human and Mouse Plasma Using Tandem High-Performance Liquid Chromatography Columns Coupled with Inductively Coupled Plasma-Mass Spectrometry

“…Using two affinity columns (a reactive blue column (19) and a heparin-Sepharose column), Deagen et al (20) succeeded in separating the selenium in plasma into three components. Harrison et al (21) also separated selenium into three main proteins by modification of the method of Deagen et al (20) and used an atomic absorption spectrometer as a selenium detector.…”