title: Interprotein metal ion exchange between cadmium-carbonic anhydrase and apo- or zinc-metallothionein.
abstract: The ligand substitution reactions of cadmium-carbonic anhydrase with EDTA and pyridine-2,6-dicarboxylic acid were compared with one in which rabbit apometallothionein was the competing metal-binding agent. This last reaction occurred more rapidly than the other two at a much smaller ratio of competing ligand to Cd-carbonic anhydrase. It was characterized as a second-order reaction, first-order in Cd-carbonic anhydrase and in apometallothionein, having a rate constant of 5.8 +/- 0.1 M-1 s-1 at 25 degrees C and pH 7.4 in Tris.HCl buffer and 0.1 M KCl. At 25 degrees C, Zn7-metallothionein also exchanged metal ions with Cd-carbonic anhydrase with a rate constant of 0.33 +/- 0.02 M-1 s-1 to reconstitute enzymatically active protein. Cd-carbonic anhydrase reacted within the time of mixing with the peptide sequence 49-61 of rabbit metallothionein 2 which contains four cysteinyl residues, leading to the exchange of most of the Cd2+ into the peptide. At pH 7.4 and 25 degrees C, Cd2+ has higher affinity for apometallothionein than for the apo-peptide.
authors.affiliation: Department of Chemistry, University of Wisconsin-Milwaukee 53201, USA.
authors.forename: J
authors.initials: J
authors.lastname: Ejnik
authors.forename: A
authors.initials: A
authors.lastname: Muñoz
authors.forename: T
authors.initials: T
authors.lastname: Gan
authors.forename: C F
authors.initials: CF
authors.lastname: Shaw
authors.forename: D H
authors.initials: DH
authors.lastname: Petering
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002104:Cadmium / Q000737:chemistry*; D002256:Carbonic Anhydrases / Q000737:chemistry* / Q000378:metabolism; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008024:Ligands; D008668:Metallothionein / Q000737:chemistry* / Q000378:metabolism; D011817:Rabbits; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008024:Ligands; C021267:zinc thionein; D002104:Cadmium; D008668:Metallothionein; D002256:Carbonic Anhydrases; D015032:Zinc