Open AccessCharacterization of the Reaction between Ferrocytochrome c and Cytochrome c Oxidase
Author(s) -
ANDRÉASSON LarsErik
Publication year - 1975
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1975.tb04102.x
Subject(s) - cytochrome c oxidase , cytochrome , chemistry , cytochrome c , cytochrome c peroxidase , heme a , cytochrome c1 , heme , electron transport chain , photochemistry , coenzyme q – cytochrome c reductase , electron transport complex iv , cytochrome b , stereochemistry , biochemistry , enzyme , mitochondrion , mitochondrial dna , gene
The reaction between cytochrome c oxidase and ferrocytochrome c has been investigated by the stopped‐flow method. It has been found that only one electron acceptor, a heme group, in the oxidase is rapidly reduced by cytochrome c . The presence of N 3 − does not affect the reduction of the acceptor, which supports the hypothesis that this is identical with cytochrome a . The results are consistent with the existence of a simple equilibrium between cytochrome a and cytochrome c :with an equilibrium constant corresponding to an oxidation‐reduction potential of cytochrome a 30 mV higher than that for cytochrome c at pH 7.4. The oxidation‐reduction potential of the a 3+ / a 2+ couple, 285 mV (based on a potential of 255 mV for cytochrome c ), and the optical properties of the reduced form indicate that it is identical with neither of the reduced hemes seen in potentiometric titrations. The oxidase species resulting from the rapid reduction of cytochrome a by cytochrome c is proposed to represent a metastable intermediate state which, under anaerobic conditions, eventually is transformed into a more stable state characterized by a reduced high‐potential heme.