title: On the environment of zinc in beef heart cytochrome c oxidase: an x-ray absorption study.
abstract: The role of zinc in beef heart cytochrome c oxidase has been studied by using x-ray absorption spectroscopy, zinc depletion and secondary structure predictions of subunits of beef heart cytochrome c oxidase. The stoichiometry of zinc in cytochrome oxidase has been determined in 35 different preparations and found to be one-half of copper (Cu:Zu = 2:1). Zinc is tightly bound to this enzyme and cannot be removed by dialysis against EDTA. However, zinc could be partially (up to 50%) depleted by treating the enzyme with either dipicolinic acid or by trypsin digestion. This partial depletion of zinc does not change the O2 uptake rate. X-ray absorption spectroscopy shows that the atom is in a distorted tetrahedral environment with mostly sulfur ligands. Since subunit VIa removed by the digestion removes about one-half the zinc, a possible binding site involves the two S sites present in that subunit with an appropriate folding in a structural role.
authors.affiliation: Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia 19104.
authors.forename: A
authors.initials: A
authors.lastname: Naqui
authors.forename: L
authors.initials: L
authors.lastname: Powers
authors.forename: M
authors.initials: M
authors.lastname: Lundeen
authors.forename: A
authors.initials: A
authors.lastname: Constantinescu
authors.forename: B
authors.initials: B
authors.lastname: Chance
mesh_terms: D000818:Animals; D001665:Binding Sites; D002417:Cattle; D003545:Cysteine / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000032:analysis / Q000378:metabolism*; D009206:Myocardium / Q000201:enzymology*; D009584:Nitrogen / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010848:Picolinic Acids / Q000494:pharmacology; D011487:Protein Conformation; D013057:Spectrum Analysis; D013455:Sulfur / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism; D014965:X-Rays; D015032:Zinc / Q000032:analysis / Q000378:metabolism*
chemical_list: D004220:Disulfides; D010848:Picolinic Acids; D013455:Sulfur; D003576:Electron Transport Complex IV; D014357:Trypsin; D015032:Zinc; D003545:Cysteine; D009584:Nitrogen; D010100:Oxygen; C004860:dipicolinic acid