Three cysteine-rich proteins of molecular weight 4000 to 7000, containing 4 to 7 gram atoms of cadmium, zinc, and copper per mole were isolated from Pseudomonas putida growing in 3 mM cadmium. The three proteins were induced during different phases of growth, and the smallest (molecular weight 3600; 3 gram atoms of cadmium) was released into the medium when the cells lysed. The results of amino acid analyses and of ultraviolet, circular dichroism, electron paramagnetic resonance, and cadmium-113 nuclear magnetic resonance spectroscopy suggest a novel cadmium(II)-zinc(II)-copper(I) cluster structure for the major protein.

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Pseudomonas putida adapted to growth in 3 mM cadmium. The resistance mechanism involved complexation of cadmium in polyphosphate granules, changes in the structure of the cell membrane and induction of three cysteine-rich, low molecular weight proteins (3500-7000) containing 4 to 7 g-atoms per mole of cadmium, zinc, and copper. Each protein was produced during a different phase of growth, and the smallest protein (3500) was released into the environment when the cells lysed at the end of the exponential phase.The metal binding sites of the major protein were further characterized using a range of physical methods, including 118Cd NMR. The properties of the bacterial pseudothioneins are compared to those of metallothioneins.

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