The effect of copper loading on the distribution of copper in rat liver cytosol

Abstract

Male Sprague-Dawley rats were given daily injections of copper (2.5 mg Cu 2+/kg body wt as copper sulfate in 0.9% NaCl) for 1–10 days. Rats were sacrificed at various time intervals and the perfused livers were fractionated. Copper in the total liver and cytosol were measured and the cytosol was further examined after chromatography on Sephadex G-75. Copper accumulated predominantly in the particulate fractions of the liver after ip injection of copper; whereas 46% of the copper added in vitro was found in the cytosol. The distribution of copper within the cytosol was different when copper was added in vivo or in vitro. In the former case, as much as 60% of the copper co-chromatographed with proteins of molecular weight 11,500–14,000 (C-peak proteins) whereas in the latter case the added copper was bound to high molecular-weight proteins (>100,000). Copper loading favored the binding of copper to the C-peak proteins in rat liver cytosol. The copper in the C-peak decreased exponentially when the copper injections were terminated. Acrylamide gel electrophoresis was used to determine the protein content of cooper-containing fractions prepared using Sephadex G-75. A protein has been identified which may act as a transport protein and whose copper content depends on the degree of copper balance in the rat; i.e., it varies with the total liver copper. The nature of the copper-binding to the C-peak proteins was also discussed.