title: Intramolecular electron transfer from c heme to d1 heme in bacterial cytochrome cd1 nitrite reductase occurs over the same distances at very different rates depending on the source of the enzyme.
abstract: Intramolecular electron transfer over 12 A from heme c to heme d(1) was investigated in cytochrome cd(1) nitrite reductase from Pseudomonas aeruginosa, following reduction of the c heme by pulse radiolysis. The rate constant for the transfer is relatively slow, k = 3 s(-1). The present observations contrast with a corresponding rate of electron transfer, 1.4 x 10(3) s(-1), measured for cytochrome cd(1) from Paracoccus pantotrophus, though the relative positions of the two heme groups are the same in both enzymes. The rate of intramolecular electron transfer within the enzyme from P. aeruginosa was accelerated 10(4)-fold (1.4 x 10(4) s(-1)) by the binding of cyanide to the d(1) heme. A coordination change at the d(1) heme upon its reduction is suggested to be a major factor in determining the slow rate of electron transfer in the P. aeruginosa enzyme in the absence of cyanide.
authors.affiliation: The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan. kobayashi@sanken.osaka-u.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Kobayashi
authors.forename: A
authors.initials: A
authors.lastname: Koppenhöfer
authors.forename: S J
authors.initials: SJ
authors.lastname: Ferguson
authors.forename: N J
authors.initials: NJ
authors.lastname: Watmough
authors.forename: S
authors.initials: S
authors.lastname: Tagawa
mesh_terms: D003574:Cytochrome c Group; D003580:Cytochromes / Q000378:metabolism*; D004579:Electron Transport; D005609:Free Radicals / Q000378:metabolism; D006418:Heme / Q000031:analogs & derivatives* / Q000378:metabolism*; D007700:Kinetics; D009536:Niacinamide / Q000031:analogs & derivatives / Q000378:metabolism; D009572:Nitrite Reductases / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D010230:Paracoccus / Q000201:enzymology; D011550:Pseudomonas aeruginosa / Q000201:enzymology; D011675:Pulse Radiolysis; D013053:Spectrophotometry
chemical_list: D003574:Cytochrome c Group; D003580:Cytochromes; D005609:Free Radicals; D009536:Niacinamide; C031690:heme C; D006418:Heme; C029400:heme d1; C019315:cytochrome cd1; D010088:Oxidoreductases; D009572:Nitrite Reductases; C048228:nitrite reductase (heme); C008472:N-methylnicotinamide