title: Electron spin-lattice relaxation of the [Cu(1.5) ... Cu(1.5)] dinuclear copper center in nitrous oxide reductase.
abstract: Relaxation times have been obtained with time-domain EPR for the dinuclear mixed valence [CuA(1.5) ... CuA(1.5)[ S = 1/2 center in nitrous oxide reductase, N2OR, from Pseudomonas stutzeri, in the TN5 mutant defective in copper chromophore biosynthesis, in a synthetic mixed valence complex, and in type 1 and 2 copper complexes. Data confirmed that the intrinsic electron spin-lattice relaxation time, T1, for N2OR in the temperature range of 6-25 K is unusually short for copper centers. At best, a twofold increase of T1 from g perpendicular to g parallel was measured. Optimized fits of the saturation-recovery data were obtained using both double-exponential and stretched-exponential functions. The temperature dependence of the spin-lattice relaxation rate of mutant N2OR is about T5.0 with the stretched-exponential model or T3.3 and T3.9 for the model using the sum of two exponentials. These T1s are intrinsic to the mixed valence [CuA(1.5) ... CuA(1.5)] center, and no interaction of the second copper center in wild-type N2OR with the [CuA(1.5) ... CuA(1.5)] center has been observed. The T1 of the mixed valence center of N2OR is not only shorter than for monomeric square planar Cu(II) complexes, but also shorter than for a synthetic mixed valence complex, Cu2(N[CH2CH2NHCH2CH2NHCH2CH2]3N). The short T1 is attributed to the vibrational modes of type 1 copper and/or the metal-metal interaction in [CuA(1.5) ... CuA(1.5)].
authors.affiliation: Biophysics Research Institute, Medical College of Wisconsin, Milwaukee 53226, USA.
authors.forename: S
authors.initials: S
authors.lastname: Pfenninger
authors.forename: W E
authors.initials: WE
authors.lastname: Antholine
authors.forename: M E
authors.initials: ME
authors.lastname: Barr
authors.forename: J S
authors.initials: JS
authors.lastname: Hyde
authors.forename: P M
authors.initials: PM
authors.lastname: Kroneck
authors.forename: W G
authors.initials: WG
authors.lastname: Zumft
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D003300:Copper / Q000032:analysis*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D003576:Electron Transport Complex IV / Q000737:chemistry; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D011549:Pseudomonas / Q000201:enzymology / Q000235:genetics; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D003300:Copper; D010088:Oxidoreductases; C022763:nitrous oxide reductase; D003576:Electron Transport Complex IV