ISOLATION AND CHARACTERIZATION OF A HEAVY METAL-BINDING PROTEIN FROM A HEAVY METAL-RESISTANT STRAIN OF THIOBACILLUS SP

A cadmium-inducible, high-molecular-weight, heavy metal-binding protei n was isolated from cadmium-exposed cells of Thiobacillus sp. strain 1 3-1. The protein was purified by SDS-polyacrylamide gel electrophoresi s, and extracted from the gel and renatured. The molecular weight of t he protein was about 150 kDa and it bound 6.5, 5.2, and 1.5 gram atoms of cadmium, copper, and zinc per mole of protein, respectively. The p rotein contained abnormal levels of histidine residues and low levels of cysteine residues. Together with the physicochemical characteristic s of the protein, these results provide the first conclusive evidence for the existence of a novel type of heavy metal-binding protein in mi croorganisms.