Ligand substitution reactions of metallothioneins with EDTA and apo-carbonic anhydrase.
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.
D000818:Animals; D001051:Apoenzymes; D001059:Apoproteins; D002104:Cadmium; D002256:Carbonic Anhydrases; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D004492:Edetic Acid; D007700:Kinetics; D008024:Ligands; D008667:Metalloproteins; D008668:Metallothionein; D015032:Zinc
D001051:Apoenzymes; D001059:Apoproteins; D008024:Ligands; D008667:Metalloproteins; D002104:Cadmium; D008668:Metallothionein; D004492:Edetic Acid; D002256:Carbonic Anhydrases; D015032:Zinc