Oxidation-reduction Potential Of Cytochrome Research Articles

Oxidation-reduction potential of cytochrome [formula omitted] oxidase in mitochondria of yeast grown under various copper concentrations

Growth of copper deficient yeast cells in copper supplemented medium led to an increase in the amount of cytochrome c oxidase and cytochromes b and c . Potentiometric titration of cytochrome c oxidase showed that the oxidation-reduction midpoint potentials of cytochromes a and a 3 were, respectively, for cells grown at 56μg copper/liter: 205 ± 10, 325 ± 10; for cells grown at 140μg copper/liter, 215 ± 10, 360 ± 10; and for cells grown at 330μg copper/liter, 215 ± 10, and 345 ± 10. Data showed that the midpoint potential of cytochromes a and a 3 in yeast mitochondria was close to the value reported for rat liver and beef heart mitochondria. In addition the stimulation of cytochrome c oxidase biosynthesis in yeast by copper does not alter significantly the redox properties of the enzyme.

Changes in oxidation-reduction potential of cytochrome b observed in the presence of antimycin A

The cytochrome b of sonic particles of mitochondria or the isolated segment of the respiratory chain containing cytochromes b and c 1 (Complex III) was 80–95% reducible with Q 1H 2 (ubiquinol-5) in the presence of antimycin plus selected electron acceptors added externally (i.e., oxidants which reacted preferentially with respiratory components on the oxygen side of the point of inhibition by antimycin) such as oxygen or ferricyanide depending on whether sonic particles or isolated Complex III was used. In contrast, less than 40% of the cytochrome b was reduced by Q 1H 2 in the absence of either antimycin or the external electron acceptor. In the presence of antimycin ascorbate or mercaptoethanol, which behaved as mild reducing agents, completely inhibited the reduction of cytochrome b by Q 1H 2. Reduction of cytochrome b by varying mixtures of Q 1 and Q 1H 2 yielded data which could be fitted by potentiometric titration curves. Midpoint potentials of cytochrome b estimated from these curves obtained in the presence of antimycin and added electron acceptor gave values of E m7 = 0.15–0.19 V; whereas, E m7 values of ca. 0.05 V were obtained in the same system but without the added electron acceptor. In the absence of both antimycin and electron acceptor, titration curves corresponding to a cytochrome b with low values of E m at low potentials ( E h) but with anomalously steep slopes were obtained. The ΔE m ΔpH between pH values 6.0 and 7.0 for cytochrome b in the presence of antimycin and an electron acceptor was −0.05 V at 0 ° which corresponds to the dissociation of one proton from cytochrome b concomitant with oxidation of cytochrome b. The requirement of both antimycin and an added electron acceptor for measurement of the high potential form of cytochrome b is strongly suggestive that the state of oxidation of a component distinct from cytochrome b controls the midpoint potential of cytochrome b. Only when this component is in its oxidized form is cytochrome b in its high-potential state.

Energy dependent changes in the oxidation-reduction potential of cytochrome [formula omitted

The oxidation-reduction midpoint potential measurement of mitochondrial cytochrome b indicate that there are two chemically different species of cytochrome b in the respiratory chain. The midpoint potential of one of these species is energy dependent.

The effect of pH on the oxidation-reduction potential of cytochrome b in heart-muscle preparations

The effect of pH on the oxidation-reduction potential of cytochrome b in heart-muscle preparations

Studies on the electron transport system: XIV. The isolation and properties of soluble cytochrome c1

The isolation of a soluble form of cytochrome c 1 has been described. Cytochrome c 1 can be extracted in reasonable yields only from particles which are free of cytochrome a. Such particles when exposed to butanol in presence of deoxycholate and ammonium sulfate liberate cytochrome c 1 in either of two soluble forms and in yields of as high as 75%. At the highest purity level the hemoprotein preparation contains 14.7 mμmoles of heme per mg of protein and 15 mμmoles of iron. The absolute absorption coefficients and oxidation-reduction potential of cytochrome c 1 have been determined. Cytochrome c 1 does not replace cytochrome c in any of several catalytic assay systems. Cytochrome c 1 can also be isolated in the form of a soluble lipoprotein complex. This complex contains about 50% by weight of lipide. Duponol efficiently separates the hemoprotein from the lipoprotein with which it is complexed.