Variations in the Oxidation-Reduction Behavior of Liganded of Pseudomonas Cytochrome Oxidase.

In an effort to determine the steady-state redox properties of Pseudomonas aeruginosa cytochrome cd(1), changes in absorption spectra after the addition of excess reductant (ascorbate, FeEDTA) were monitored for degassed unliganded enzyme and samples in the presence of CO and CN(theta) in 0.1 M Tris buffer, ph = 6.0, 8.0 or 10.0. Plots of [c(2+)]/[c(3+)] vs. [d(2+)]/[d (3+)] indicate that a "pseudoequilibrium" was reached for all samples at ph = 8.0. Calculated values of delta E(d-c') the difference in reduction potential between the heme c and heme d moieties, at ph 8.0 were: -25 +- 5mV (unliganded), - 10 +- 5 mV (enzyme-CO) and -25 +- 5mV (enzyme-CN). Relative rates of heme c and heme d reduction were found to be dependent upon type of ligand, reductant and pH. Evidence for cooperative heme c-heme d interaction is discussed.