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  • Title: Ligand substitution reactions of metallothioneins with EDTA and apo-carbonic anhydrase.
    Author: Li TY, Kraker AJ, Shaw CF, Petering DH.
    Journal: Proc Natl Acad Sci U S A; 1980 Nov; 77(11):6334-8. PubMed ID: 6779278.
    Abstract:
    The reactions of Zn-, Zn,Cd-, and Cd-thioneins with EDTA and apo-carbonic anhydrase have been studied. The ligand substitution reaction of zinc with EDTA is multiphasic, having both associative and dissociative components in the rate expression. The cadmium sites are about 2 orders of magnitude less reactive. In contrast, apo-carbonic anhydrase abstracts zinc from Zn-thionein and Zn,Cd-thionein in second-order processes that are 2-3 orders of magnitude more rapid than those involving EDTA and approach the rate for unligated Zn2+ with the apo-protein. In comparison with other zinc proteins, Zn-thionein contains unusually reactive metal sites, suggesting that this protein may be a physiological zinc transfer protein, able to donate zinc to zinc-requiring apo macromolecules.
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