Isolation of a non-thionein copper-binding protein from liver of copper-injected rats.

1. The characterization of a low molecular weight, non-thionein, Cu-binding protein isolated from rat liver is reported. The protein was isolated following chronic administration of Cu(NO3)2 using a combination of Sephadex G75 and Sephadex DEAE A-25 chromatography. The protein did not bind to fully equilibrated Sephadex DEAE which formed the basis of the isolation procedure. 2. The final protein pereparation was found to be homogenous by a variety of electrophoretic techniques and was distinguished from metallothionein on the basis of its behaviour on ion exhcange and electrophoretic systems, spectral properties, and amino acid composition and metal content. It contains 6.8% cysteine and was found to bind Cu in a ration of 1.5:1 based on a molecular weight of 11 000. 3. These results confirm the necessity to use techniques other than gel filtration alone to obtain adequate separation of low molecular weight metal-binding protein fractions.