The nature of zinc in cytochrome c oxidase.
The zinc ion in bovine heart cytochrome c oxidase can be completely depleted from the enzyme with mercuric chloride without denaturing the protein. The metal atom stoichiometry of 5Cu/4Fe/0Zn/2Mg obtained for the enzyme following HgCl2 treatment indicates that this depletion is highly selective. Zinc depletion exposes one cysteine on subunit VIa and one cysteine on subunit VIb for N-iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylene-diamine (1,5-I-AEDANS) labelling, suggesting that the zinc plays a structural role in the protein by providing a bridge between these two subunits. Although the treatment of cytochrome c oxidase with mercuric chloride inhibits the steady-state activity of the enzyme, subsequent removal of the Hg2+ bound to cysteine residues by 1,5-I-AEDANS significantly reverses the inhibition. This latter result indicates that the removal of the zinc itself does not alter the steady-state activity of the enzyme.
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A. A. Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena 91125.
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D000818:Animals; D002417:Cattle; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D015394:Molecular Structure; D015032:Zinc / Q000737:chemistry / Q000502:physiology*
D003576:Electron Transport Complex IV; D015032:Zinc