Basal metallothionein in tumors: widespread presence of apoprotein

A survey has been conducted of solid and ascites tumors from mice and solid tumors in rats for the presence of metallothionein or metallothionein-like protein. In most tumors, a positive identification was made on the basis of Sephadex G-75 and HPLC-DEAE chromatography followed by competitive radioimmunoassay for metallothionein. Apometallothionein was revealed in a number of tumors for the first time by comparing the Sephadex G-75 chromatographic profiles of Zn in native cytosol and Cd in cytosol incubated briefly with CdCl2 to saturate free binding sites on the protein before Sephadex G-75 chromatography. In two cases unsaturation of metallothionein was correlated with a lack of zinc in the ascites fluid which supplies the tumor with zinc.