Partial Characterization of a Cadmium-binding Protein from the Roots of Cadmium-treated Tomato

A Cd-binding protein has been isolated from the roots of Cd-treated tomato plants cv. Rutgers. Almost all the Cd from a high-speed supernatant fraction was recovered in a 10,000-dalton fraction from a gel filtration column coincident with 250-nanometer absorbing material. DEAE-cellulose chromatography of this 10,000-dalton material yielded one major component, which eluted at 0.34 molar NaCl, had an absorption spectrum characteristic of metallothionein, and showed absorption changes upon acidification typical of metallothionein. Although the Cd-binding protein did not behave like metallothioneins from animal sources during gel electrophoresis at pH 8.9, a single band containing Cd and staining with Coomassie brilliant blue could be detected following electrophoresis at pH 6.9. Synthesis of the Cd-binding protein appeared to be "induced" by treatment of the plants with Cd(2+).