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Reaction of dioxygen with a mixed-valence copper(I)-copper(II) dinuclear complex
52 ABSTRACTS
p22
CRYSTAL STRUCTURE OF MET121GLU AZURIN EXPLAINS pH DEPENDENCE IN SPECTROSCOPY B. G&an Karlsson, Institutionen flir Biokemi och Biofisik, Chalmers Tekniska Hiigskola, S-412 96 Giiteborg, SWEDEN
The Metl21Glu azurin mutant has been crystallised and the structure determined
in collaboration with the groups of Dr. Lennart SjSlin and Prof. Robert Huber. In the crystal structure a carboxylate oxygen of Glu121 is coordinated to the metal, and the titration of this residue gives rise to a number of interesting, pH dependent properties: The strong S(Cys)-Cu ligand-to-metal charge transfer bands are blue-shifted and their intensities reversed, the ERR signal changes from type 1 copper to a new form of protein-bound copper and the redox potential changes from 372 mV to 220 mV as pH is increased from pH 4 to pH 7. The pK (4.9) of Glu121 is anomalous for a carboxylate group coordinated to a metal.
p23 ~~XXTION
CATALASE GENE EXPRESSION BY p.I. and V. Culotta, School of Hygiene and Public Health, JdiunsHopkins Uniwrsity, Baltimore, MD 21205. Yeast cells respond to toxic copper by increasing cellular catalase levels. We have investigated whether this regulation occurs at the level of gene transcription, and whether the peroxisomal (CAT A) or cytosolic (CAT T) catalases are involved. Our data indicates that while the CAT A gene is not regulated by copper, CAT T mRNA levels are induced by the metal. Surprisingly, this induction is independent of ACE1 , the “Cu-Fist” transcription factor that regulates yeast metallothionein and Cu/Zn superoxide dismutase.
p24
?F
REACTION OF DIOXYGEN WITH A MIXED-VALENCE COPPER(I)-COPPER(II) DINUCLEAR COMPLEX Mohamroof Tal& and Kenneth D. Karlin, Dept. of Chemistry,
The Johns Hopkins University, Baltimore, MD 21218 USA
Few superoxo-Cu(II) complexes have been described, but these are of interest as being part of the first step in dioxygen reduction by Cu(I), and as biological intermediates. We have recently initated studies of unsymmetrical dinucleating ligand complexes,1 and we find that the phenoxo-bridged dicopper(I) complex [Cuz(UN-0-)]+ (1) can be oxidized with ferrocinium cation to give a mixed valence complex [CS.@N-0-)J2+ (2). While 1 reacts with 02 giving a peroxo-bridged complex [Cuz(UN-0-)(Q2)]+ (3), 2 reacts reversibly with 02 giving an adduct, a superoxo dicopper(II) complex [Cu2(UN-0-)(O#+ (4); this can also be formed directly from 3 by chemical oxidation with Ag+. Additional physical characterization of 3 and 4 will be described. 1. M. S. Nasir et. al., J. Am. Chem. Sot., 113, 698 (1991).
p22
CRYSTAL STRUCTURE OF MET121GLU AZURIN EXPLAINS pH DEPENDENCE IN SPECTROSCOPY B. G&an Karlsson, Institutionen flir Biokemi och Biofisik, Chalmers Tekniska Hiigskola, S-412 96 Giiteborg, SWEDEN
The Metl21Glu azurin mutant has been crystallised and the structure determined
in collaboration with the groups of Dr. Lennart SjSlin and Prof. Robert Huber. In the crystal structure a carboxylate oxygen of Glu121 is coordinated to the metal, and the titration of this residue gives rise to a number of interesting, pH dependent properties: The strong S(Cys)-Cu ligand-to-metal charge transfer bands are blue-shifted and their intensities reversed, the ERR signal changes from type 1 copper to a new form of protein-bound copper and the redox potential changes from 372 mV to 220 mV as pH is increased from pH 4 to pH 7. The pK (4.9) of Glu121 is anomalous for a carboxylate group coordinated to a metal.
p23 ~~XXTION
CATALASE GENE EXPRESSION BY p.I. and V. Culotta, School of Hygiene and Public Health, JdiunsHopkins Uniwrsity, Baltimore, MD 21205. Yeast cells respond to toxic copper by increasing cellular catalase levels. We have investigated whether this regulation occurs at the level of gene transcription, and whether the peroxisomal (CAT A) or cytosolic (CAT T) catalases are involved. Our data indicates that while the CAT A gene is not regulated by copper, CAT T mRNA levels are induced by the metal. Surprisingly, this induction is independent of ACE1 , the “Cu-Fist” transcription factor that regulates yeast metallothionein and Cu/Zn superoxide dismutase.
p24
?F
REACTION OF DIOXYGEN WITH A MIXED-VALENCE COPPER(I)-COPPER(II) DINUCLEAR COMPLEX Mohamroof Tal& and Kenneth D. Karlin, Dept. of Chemistry,
The Johns Hopkins University, Baltimore, MD 21218 USA
Few superoxo-Cu(II) complexes have been described, but these are of interest as being part of the first step in dioxygen reduction by Cu(I), and as biological intermediates. We have recently initated studies of unsymmetrical dinucleating ligand complexes,1 and we find that the phenoxo-bridged dicopper(I) complex [Cuz(UN-0-)]+ (1) can be oxidized with ferrocinium cation to give a mixed valence complex [CS.@N-0-)J2+ (2). While 1 reacts with 02 giving a peroxo-bridged complex [Cuz(UN-0-)(Q2)]+ (3), 2 reacts reversibly with 02 giving an adduct, a superoxo dicopper(II) complex [Cu2(UN-0-)(O#+ (4); this can also be formed directly from 3 by chemical oxidation with Ag+. Additional physical characterization of 3 and 4 will be described. 1. M. S. Nasir et. al., J. Am. Chem. Sot., 113, 698 (1991).