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Coulometric and Potentiometric Evaluation of the Redox Components of Cytochrome C Oxidase in Situ

Coulometric and Potentiometric Evaluation of the Redox Components of Cytochrome C Oxidase in Situ

D F Wilson, D Nelson

Biochim Biophys Acta. 1982 Jun 18;680(3):233-41.

PMID: 6285964

Abstract:

A new coulometric-potentiometric titration cuvette is described which permits accurate measurements of oxidation-reduction components in membranous systems. This cuvette has been utilized to measure the properties of cytochrome c oxidase in intact membranes of pigeon breast muscle mitochondria. The reducing equivalents accepted and donated by the portion of the respiratory chain with half-reduction potentials greater than 200 mV are equal to those required for the known components (cytochrome a3 and the high-potential copper plus cytochrome a, 'visible copper', cytochrome c1, cytochrome c, and the Rieske iron-sulfur protein). Titrations in the presence of CO show that formation of the reduced cytochrome a3-CO complex requires two reducing equivalents per cytochrome a3 (coulometric titration). Potentiometric titrations indicate (Lindsay, J.G., Owen, C.S. and Wilson, D.F. (1975) Arch. Biochem. Biophys. 169, 492--505) that both cytochromes a3 and the high-potential copper must be reduced in order to form the CO complex (n = 2.0 with a CO concentration-dependent half-reduction potential, Em). By contrast, titrations in the presence of azide show that the Em value of the high-potential copper is unchanged by the presence of azide and thus azide binds with nearly equal affinity whether the copper is reduced or oxidized.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP9007436-A	Cytochrome c from pigeon breast muscle		9007-43-6	Price

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