Kinetics of conformation change in cyanometmyoglobin following electron transfer monitored by magnetically induced circular dichroism spectrometry.

The characterization of the dynamics of conformational changes that accompany the ligand binding and dissociation reactions of myoglobin may provide insights into the events that control the physiological function of this oxygen storage protein. The cyanometmyoglobin system was chosen for this study because cyanide binds to the metmyoglobin state and dissociates upon reduction. The potential step spectroelectrochemical method was used here because the rate of cyanometmyoglobin reduction at an electrode can be controlled so that the rate of dissociation of the reduced cyanomyoglobin can then be followed.

Evidence for the role of myoglobin in facilitating oxygen transport.

Cyclic voltammetric studies of the heterogeneous electron-transfer reactions of myoglobin under aerobic and anaerobic conditions are reported. Evidence for a role of myoglobin that has not been previously measured directly, namely, facilitation of oxygen transport, is presented. It is suggested that one molecule of oxygen can be contained within the structure of the oxidized form of myoglobin, but is not co-ordinated to the heme iron. Reduced myoglobin binds one molecule of oxygen to the heme iron but no reports have been found that suggest that the oxidized form of myoglobin binds to, or contains a molecule of, oxygen.

Direct electron transfer reactions of cytochrome c553 from Desulfovibrio vulgaris Hildenborough at indium oxide electrodes.

The direct, heterogeneous, electron transfer reactions of cytochrome c553 from Desulfovibrio vulgaris Hildenborough have been studied at indium oxide optically transparent electrodes. These reactions have been studied using cyclic voltammetry and derivative cyclic voltabsorptometry and the kinetics of heterogeneous electron transfer is quasi-reversible. The thermodynamics and kinetics of electron transfer by this molecule can be studied at this electrode surface without the need for surface modification or the addition of surface promoters or mediators.

Cytochrome c3 from the sulfate-reducing anaerobe Desulfovibrio africanus Benghazi: purification and properties.

Cytochrome c3 was purified from Desulfovibrio africanus Benghazi by extraction with alkaline deoxyribonuclease, fractionation with ammonium sulfate, batch elution from carboxymethyl Sephadex followed by chromatography on the same resin, and gel filtration on Sephadex G-75. The preparation was judge homogeneous by a variety of criteria. The molecular weight was determined in an analytical ultracentrifuge, and values between 14,400 and 15,490 were obtained, depending upon the presumed value of partial specific volume. Gel filtration on a calibrated column of Sephadex G-75 gave a value of 14,900 daltons. The amino acid composition was very similar to that observed for the cytochrome from other species of Desulfovibrio, with the exception of increased levels of ThR and PhE. S-Carboxymethylation of the protein before and after heme removal by HgCl2 demonstrated eight Cys molecules involved in heme binding or four heme sites per molecule. Titration with sodium dithionite under N2 gave an electrochemical potential (E' 0) of -276 mV relative to the normal hydrogen electrode. Electrochemical titration of the cytochrome gave a Nernst plot with two linear regions with E' 0 values of -0.376 and -0.534 V. The spectra produced at various potentials exhibited shifts in isosbestic points upon reduction, suggesting changes in conformation during the reaction.

Redox titration of fluorescence yield of photosystem II.

The variable fluorescence yield of photosystem II is dependent on the redox state of the fluorescence quencher molecule or the primary electron acceptor of the system. We have carried out redox titrations of fluorescence yield of a photochemically active photosystem-II reaction-center particle and have measured the redox potential of the photosystem-II primary acceptor.During reductive titrations using dithionite as the reductant, only a single quenching transition was observed. For instance, at pH 7.0, the midpoint potential of the fluorescence transition is -325 mV, and those at a pH between 6.0 and 7.5 are consistent with a pH dependence of about 60 mV/pH unit. At a given pH, the midpoint potential of the transition closely corresponds to that of the most negative transition previously measured in unfractionated chloroplasts (both by chemical reductive titration). Oxidative titrations using ferricyanide as the oxidant yielded hysteresis in the titration curves.Similar changes in fluorescence yield were observed in redox titrations by electrochemical reduction or oxidation. Electrochemical reductive and oxidative titrations yielded reversible transitions, contrary to the hysteresis observed during chemical oxidative titration. From coulometric-titration data, we have estimated that most likely one electron is involved in the redox transition of the fluorescence-quencher or primary-electron-acceptor molecule of photosystem II. These findings are consistent with the current proposal that a membrane-bound plastoquinone functions as the primary acceptor of photosystem II.