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Kinetic control of internal electron transfer in cytochrome c oxidase
Author(s) -
Brunori Maurizio,
Giuffré Alessandro,
D'Itri Emilio,
Sarti Paolo
Publication year - 1998
Publication title -
biofactors
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.204
H-Index - 94
eISSN - 1872-8081
pISSN - 0951-6433
DOI - 10.1002/biof.5520080304
Subject(s) - chemistry , adduct , cytochrome c oxidase , redox , ruthenium , electron transfer , heme a , heme , photochemistry , kinetics , cytochrome c , oxidase test , electron transport chain , enzyme , stereochemistry , medicinal chemistry , inorganic chemistry , catalysis , biochemistry , mitochondrion , organic chemistry , physics , quantum mechanics
Two alternative hypotheses have been proposed to account for the relatively slow (ms) internal eT observed in the oxidized cyt c oxidase. The thermodynamic control hypothesis states that eT between cyt a and a 3 is very fast (μs), but the apparent reduction of cyt a 3 is slow because thermodynamics favors reduced cyt a. Whereas the kinetic control hypothesis states that inter‐heme eT is intrinsically slow (ms), for the oxidized binuclear center. Monitoring by stopped flow the anaerobic reduction of the oxidized enzyme by ruthenium hexamine in the absence and presence of CO or NO, used as “trapping” ligands for cyt a 3 2+ , we found that the rate of formation of the cyt a 3 2+ —NO adduct ( k ′ ≈ 20–25 s −1 ) is independent of the concentration of ruthenium hexamine and NO. We conclude that in the oxidized enzyme the two hemes are not in very rapid redox equilibrium and internal eT is kinetically controlled.