Among the potentially toxic metals that may be most nutritious and beneficial is zinc, but zinc's reaction in our body can be made far less predictable by other metal toxins. Since the metals of concern all poison sulfur biochemistry, reacting with sulfides or causing shifts in chemistry like enhancing the formation of enols, then even modest toxicity in each can add up or be synergistic in being overall unexpectedly very toxic. This is made cogent by the interactions of many toxic metals with the protective protein, metallothionine. This protein has large amounts of cysteine in its amino acid backbone, which appears designed to bind up and buffer inadvertent metal toxin exposure.Thus, lLess toxic metals in excess sometimes can cause release of more toxic metals.