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Media type:
E-Article
Title:
Oxygen ``Pulsed'' Cytochrome c Oxidase: Functional Properties and Catalytic Relevance
Contributor:
Antonini, Eraldo;
Brunori, Maurizio;
Colosimo, Alfredo;
Greenwood, Colin;
Wilson, Michael T.
imprint:
National Academy of Sciences of the United States of America, 1977
Published in:Proceedings of the National Academy of Sciences of the United States of America
Language:
English
ISSN:
0027-8424
Origination:
Footnote:
Description:
<p>The kinetics of the reaction of cytochrome c with solubilized mammalian cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) has been studied by a stopped-flow technique under two different experimental situations: (i) the completely oxidized enzyme (resting oxidase as obtained from the preparation) was mixed with reduced cytochrome c, and (ii) the completely reduced enzyme in the presence of reduced cytochrome c was exposed to a ``pulse'' of O<sub>2</sub>(pulsed oxidase). Both sets of experiments were performed with either ``limiting'' or ``excess'' O<sub>2</sub>(relative to oxidase), in the presence or absence of CO. Both the pre-steady-state events and the steady-state kinetics of cytochrome oxidase are found to be different in the two cases. This shows that the product of the reaction of fully reduced oxidase with O<sub>2</sub>(pulsed oxidase) is functionally different from the oxidase as prepared (resting oxidase). These differences are interpreted with the assumption of a different rate of intramolecular electron transfer in the pulsed and resting oxidases. Implications of these experimental findings are discussed in the general framework of a tentative model for the catalytic cycle of the oxidase.</p>