Trapping of an intermediate in the oxidation-reduction cycle of cytochrome d in Escherichia coli

Effects of pH and detergent on the kinetic and electrochemical properties of the purified cytochrome d terminal oxidase complex of Escherichia coli

The cytochrome d terminal oxidase complex is one of the two terminal oxidases in the aerobic respiratory chain of Escherichia coli. In this paper, effects of pH and detergent on the electrochemical and kinetic properties of the enzyme are investigated. There are two significant conclusions. (1) The oxidation-reduction midpoint potential of the cytochrome b-558 component is sensitive to the detergent used to solubilize the complex. In particular, it is shown that octylglucoside and cholate cause a large decrease in the midpoint potential of cytochrome b-558, while they also result in the reversible inactivation of the oxidase. (2) The midpoint potentials of the cytochrome b-558, a1 and d components are sensitive to pH. More acidic solutions result in stabilizing the reduced forms of the redox-active groups, i.e., raising their midpoint potentials. This may be significant in view of the fact that it has been demonstrated that this enzyme catalyzes an electrogenic reaction and appears to function as a proton pump.

Cytochrome a620 in Tetrahymena pyriformis. Reactions with carbon monoxide and oxygen at subzero temperatures and photochemical action spectra

1. Mitochondria-enriched fractions of the ciliate protozoan Tetrahymena pyriformis ST contained CO-reacting cytochromes b560 and a620. 2. A non-photodissociable oxygen-containing compound of cytochrome a620 was formed in whole cell suspensions at -114 degrees C after photolysis of CO in the presence of 200 microM-O2. 3. Electron transport, indicated by the oxidation of cytochrome a620 and cytochrome c, occurred at temperatures higher than -72 degrees C. 4. Photochemical action spectra for the relief of respiratory inhibition of whole cells by CO obtained by using a liquid dye laser indicate that the only CO-reacting terminal oxidase detectable was cytochrome a620. 5. It is concluded that the alternative electron transport chains in this organism utilize non-cytochrome terminal oxidases.