Electron spin-lattice relaxation of the [Cu(1.5) ... Cu(1.5)] dinuclear copper center in nitrous oxide reductase

• Published in: Biophysical journal Vol. 69; no. 6; pp. 2761 - 2769
• Main Authors: Pfenninger, S., Antholine, W.E., Barr, M.E., Hyde, J.S., Kroneck, P.M., Zumft, W.G.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.12.1995
• Subjects: Amino Acid Sequence; Animals; Binding Sites; Cattle; Copper - analysis; Electron Spin Resonance Spectroscopy - methods; Electron Transport Complex IV - chemistry; Kinetics; Molecular Sequence Data; Mutation; Oxidoreductases - chemistry; Oxidoreductases - metabolism; Protein Structure, Secondary; Pseudomonas - enzymology; Pseudomonas - genetics; Temperature; Thermodynamics; Time Factors
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(95)80149-9

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)].