Search

The stoichiometry of the proton uptake reaction was determined to be approximately 1.3 + or - 0.3, 1.4 + or - 0.3 and 1.6 + or - 0.5 protons per enzyme at pH values of 6.5, 7.5, and 8.5, respectively. The electron transfer values between CUA and heme a was limited by proton uptake on a time scale of 90 microseconds. The results were derived from an investigation of proton and electron transfer during the reaction of solubilized fully reduced bovine heart cytochrome c oxidase with molecular hydrogen using the flow-flash technique.

Cytochrome c oxidase was illuminated with a deuterium lamp to determine the spectral characteristics of the enzyme in the presence of oxygen. Results reveal that the light-induced changes and the visible absorption spectra of oxidized cytochrome c oxidase are pH-dependent. Furthermore, the spectral shifts are similar to those involved in oxidized enzyme and hydrogen peroxide reactions. It is also found that the spectral shifts produces a mixture of species with absorbance maxima at 607 and 580 nm when referenced against the oxidized enzyme.

Peroxy and ferryl species are formed as intermediates during the reduction of dioxygen by cytochrome c oxidase at room temperature. The ferrous-oxy compound attains maximum concentration 30 micro seconds after photolysis, and decays into the peroxy species. The peroxy species decays into the ferryl intermediate which has a peak at 578 nm. The maximum concentration of the ferryl species is reached after 310 micro seconds of photolysis. The agreement between the results from theoretical and experimental spectra confirms the presence of peroxy and ferryl intermediates.

Electrocatalytic voltammetry reveals that succinate dehydrogenase catalyzes fumarate reduction at pH values below 7.7. The catalysis takes place under reversible conditions at a physiological temperature of 38 degrees centigrade. A more negative potential decreases the catalytic activity drastically. This effect is related to two-electron/two-proton reduction of flavin adenine dinucleotide. A study measures the catalytic activity over a range of potentials, and describes the energetics and kinetics of catalyzed electron transport.

A study on the synthesis of several dicobalt mu-peroxo-bridged complexes for photochemical reactivity shows that the complex (mu-peroxo)(mu-hydroxo)bis bis(bipyridyl)cobalt(III) vents dioxygen when irradiated with 355-nm laser light with a quantum yield of 0.04. A linear relation between the spectral changes and the oxygen production suggests that O2 is liberated on the same time scale. Furthermore, oxyhemoglobin is formed from deoxyhemoglobin upon dissociation of the (mu-peroxo)(mu-hydroxo)bis [bis(bipyridyl)cobalt(III)] complex, proving that O2 is the primary photo product.

Analysis of the visible and near-infrared transient differences spectra of the photolytic intermediate of cytochrome C oxidase by global exponential fitting procedure reveals the presence of five intermediates. Mechanistic study suggests that the first step involves a conformational change at cytochrome a3. Second step involves the 1:1 electron transfer from cytochrome a3 to cytochrome a. Oxidation of cytochrome a occurs in the third step. Absorption spectrum of oxidized cytochrome a3 is significantly influenced by the redox state of CuB.

Fumarate reductase (Escherichia coli) can be immobilized in a highly electroactive condition at an electrode and still maintain native catalytic traits. The membrane-extrinsic FrdAB element adsorbs to monolayer coverage at edge-oriented pyrolytic graphite and catalyzes reduction of fumarate or oxidation of succinate, based on the electrode potential. Cyclic voltammetry can record the reversible redox changes of centers in the enzyme in the absence of substrates.

The redox-coupled binding of a thiolate ligand to an Fe-S protein cluster has been characterized by voltammetry. The protein ligand of Ferrodoxin III which contains seven cysteines capable of ligating both (4Fe-4S) and (3Fe-4S) clusters, utilized for characterization has been isolated from the Desulfovibrio africanus strain. The kinetics and equilibrium constants of the ligation has also been measured. Findings show no definite interaction betweeen either of the protein clusters and thiolate. However, voltammetric characterization demonstrated the time-separated coupling of electron transfer to conformational change.

A voltammetric analysis of proton-gated electron transfer in a mutant ferredoxin reveals that oxidation of the (3Fe-4S) cluster of Azobacter vinelandii ferredoxin I is inhibited by modification of aspartate-15 (D15) to asparagine. Redox kinetics analyses confirm the distinct behavior for native and D15N forms.

Presents a voltammetric study of the redox kinetics of a mutant ferredoxin that appears to be kinetically defective with regard to coupled proton transfer. Electrochemical potential-reversal method; 7Fe ferredoxin I from Azotobacter vinelandii.

The reaction between bovine heart cytochrome c oxidase and dioxygen was monitored at room temperature in the visible and Soret regions following photolysis of the mixed-valence CO-bound enzyme. Time-resolved optical absorption difference spectra were collected between 50 ns and 1.7 ms by a gated multichannel analyzer. Singular value decomposition and global exponential fitting resolved three processes with apparent lifetimes of 2.2±0.5, 17±4 and 160±30 μs. The spectra of the intermediates were extracted based on a sequential kinetic mechanism and compared to the corresponding intermediate spectra observed during the reaction of the fully reduced enzyme with dioxygen. The first process is associated with a conformational change at heme a3 upon dissociation of CO from CuB+ and concomitant back-electron transfer from heme a3 to heme a. This is followed by O2 binding to heme a3 forming compound A (AM), with a spectrum identical to that observed upon O2 binding to heme a3 in the fully reduced enzyme (AR). Intermediate AM decays into PM, the spectrum of which is equivalent to that of the 607 nm form, generated upon addition of H2O2 to the oxidized enzyme at alkaline pH values (PH). However, the spectrum of PM is significantly different from the corresponding intermediate observed upon the reaction of dioxygen with the fully reduced enzyme (PR). The spectral differences between PM and PR may arise from the different number of redox equivalents at the binuclear site, with a tyrosine radical in the PM state, and tyrosine or tyrosinate in PR, or may be the consequence of a more complex reaction mechanism in the case of the fully reduced enzyme. [Copyright &y& Elsevier]