Jul 20, 2002

Intramolecular electron transfer in cytochrome cd(1) nitrite reductase from Pseudomonas stutzeri; kinetics and thermodynamics

Biophysical Chemistry
O FarverI Pecht


Cytochrome cd(1) nitrite reductase from Pseudomonas stutzeri catalyzes the one electron reduction of nitrite to nitric oxide. It is a homodimer, each monomer containing one heme-c and one heme-d(1), the former being the electron uptake site while the latter is the nitrite reduction site. Hence, internal electron transfer between these sites is an inherent element in the catalytic cycle of this enzyme. We have investigated the internal electron transfer reaction employing pulse radiolytically produced N-methyl nicotinamide radicals as reductant which reacts solely with the heme-c in an essentially diffusion controlled process. Following this initial step, the reduction equivalent is equilibrating between the c and d(1) heme sites in a unimolecular process (k=23 s(-1), 298 K, pH 7.0) and an equilibrium constant of 1.0. The temperature dependence of this internal electron transfer process has been determined over a 277-313 K temperature range and yielded both equilibrium standard enthalpy and entropy changes as well as activation parameters of the specific rate constants. The significance of these parameters obtained at low degree of reduction of the enzyme is discussed and compared with earlier studies on cd(1) nitrite reductases...Continue Reading

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Mentioned in this Paper

Nicotinamide Assay
Cytochrome c Oxidase Subunit VIa
Cytochrome cd1 nitrite reductase
Nitrite Reductase
Electron Transport
Radicals (chemistry)
Pseudomonas stutzeri

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