title: Interaction of copper with cysteine: stability of cuprous complexes and catalytic role of cupric ions in anaerobic thiol oxidation.
abstract: Copper complexes with cysteine have been investigated by optical spectroscopy, NMR and ESR. Cuprous ions strongly bind to the thiol group of Cys forming polymeric species with bridging thiolate sulfur according to a stoichiometry of about 1:1.2 and stability constant of the order of 10(10) M(-1). Cupric ions in the presence of cysteine, up to a ratio 0.45:1, are reduced to Cu(I) with stoichiometric production of cystine. The Cu(I) produced by this reaction is complexed by the excess of Cys. Trace amounts of Cu(II) exceeding the ratio 0.45:1 induce fast and complete oxidation of the Cys-Cu(I) complex to cystine with concomitant production of Cu(0) which precipitates. The experimental data are consistent with a mechanism by which Cu(II) oxidizes the complex Cys-Cu(I) to cystine producing aqueous Cu(I) which undergoes dismutation regenerating Cu(II). According to this mechanism the uncomplexed Cu(II) plays a catalytic oxidative role in the absence of molecular oxygen. The biological significance of these reactions is discussed.
authors.affiliation: Dipartimento di Chimica Biologica, Università di Padova, Padova, Italy.
authors.forename: Adelio
authors.initials: A
authors.lastname: Rigo
authors.forename: Alessandra
authors.initials: A
authors.lastname: Corazza
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: di Paolo
authors.forename: Monica
authors.initials: M
authors.lastname: Rossetto
authors.forename: Raffaella
authors.initials: R
authors.lastname: Ugolini
authors.forename: Marina
authors.initials: M
authors.lastname: Scarpa
mesh_terms: D002384:Catalysis; D003300:Copper / Q000737:chemistry* / Q000378:metabolism*; D003545:Cysteine / Q000737:chemistry* / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D013057:Spectrum Analysis; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000378:metabolism; D017186:Titrimetry
chemical_list: D013438:Sulfhydryl Compounds; D003300:Copper; D003545:Cysteine; D010100:Oxygen