Cadmium-binding protein in roots of maize

Abstract

A partially purified cadmium (Cd) binding protein was isolated from roots of maize (Zea mays L.). Proteins were first separated on the anion exchanger QAE-Sephadex A-25. The major Cd fraction, comprising as much as 85% of the buffer-soluble Cd, was then chromatographed on Sephadex G-75 in 1 M KCl buffer. The resulting partially purified protein preparation was dark brown, had an apparent molecular weight of 3100, and bound 2 g atoms Cd/mol. The cysteine content was 40%; the Cd:cysteine ratio was 1:6. The Cd–thiolate chromophore was evident from spectroscopic measurements. The roots produced the metallothioneinlike protein after they were exposed to 3 μM Cd for 4 days.