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The rate‐limiting step and nonhyperbolic kinetics in the oxidation of ferrocytochrome c catalyzed by cytochrome c oxidase
Author(s) -
Brzezinski Peter,
Thörnström Per-Eric,
G. Malmström Bo
Publication year - 1986
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(86)80040-0
Subject(s) - chemistry , cytochrome c , electron transfer , cytochrome , cytochrome c oxidase , kinetics , photochemistry , intramolecular force , electron transport chain , cytochrome c1 , coenzyme q – cytochrome c reductase , stereochemistry , organic chemistry , biochemistry , enzyme , mitochondrion , physics , quantum mechanics
The level of reduction of cytochrome a and cu a during the oxidation of ferrocytochrome c has been determined in stopped‐flow experiments. Both components are partially reduced but become progressively more oxidized as the reaction proceeds. When all cytochrome c has been oxidized, cu a is also completely oxidized, whereas cytochrome a is still partially reduced. These results can be simulated on the basis of a model which requires that the intramolecular electron transfer from cytochrome a and cu a to cytochrome a 3 ‐Cu b is a two‐electron process and, in addition, that the binding of oxidized cytochrome c to the electron‐transfer site decreases the rate constants for intramolecular electron transfer from cytochrome a . The first requirement is related to the function of the oxidase as a proton pump. Product dissociation is not by itself rate‐limiting, making it less likely that the source of the nonhyperbolic substrate kinetics is an effect on this step from electrostatic interaction with ferricytochrome c bound to a second site. It is pointed out that nonhyperbolic kinetics is, in fact, an intrinsic property of ion pumps.