Structure and Function of Transcuprein, in Transport of Copper by Mammalian Blood Plasma

Abstract

Using 67Cu of high specific activity, we have shown previously in rats that copper entering the blood from the intestine (or directly by intraveneous injection) immediately binds to 2 components in the blood plasma (Weiss and Linder, 1985). These are albumin, which has for some time been known to have a single, high affinity site for Cu binding (Lau and Sarkar, 1971), and another, new plasma protein we have named transcuprein that has an apparent molecular weight of 270 kDa (Weiss and Linder, 1985). Transcuprein rapidly exchanges copper with albumin, and the specific activity of copper on both of these proteins diminishes in parallel, and very fast, after administration of radioactive tracer. Depletion of newly absorbed copper bound to albumin and transcuprein with time is accompanied a deposition of copper in liver and kidney. The kinetics of these changes are consistent with those of a precursor/product relationship, implying that transcuprein and albumin are delivering Cu to both of these organs after absorption from the diet. Transcuprein, ceruloplasmin, and albumin (as well as components of low molecular weight binding Cu) may be fractionated on columns of Sephadex G150. “Profiles” of rat and human plasma fractionated in this manner have 10–15% of the Cu associated with transcuprein. An approximately equal quantity is associated with albumin, and the remainder is mainly associated with ceruloplasmin, but about 10% is with low molecular weight components (Wirth and Linder, 1985). Further work on the structure and function of the new Cu transport protein is described below.