1,721,001 research outputs found
The proton/electron coupling ratio at heme a and CuA in bovine heart cytochrome c oxidase
No full textMeasurements of the H+/heme a, CuA ratios for proton−electron coupling at these centers (redox Bohr effect) in CO-inhibited cytochrome c oxidase purified from bovine heart mitochondria, both in the soluble state and reconstituted in liposomes, are presented. In the soluble oxidase, the H+/heme a, CuA ratios were experimentally determined upon oxidation by ferricyanide of these centers as well as upon their reduction by hexammineruthenium(II). These measurements showed that in order to obtain H+/heme a, CuA ratios approaching 1, one-step full oxidation of both metal centers by ferricyanide had to be induced by a stoicheiometric amount of the oxidant. Partial stepwise oxidation or reduction of heme a and CuA did produce H+/heme a, CuA ratios significantly lower or higher than 1, respectively. The experimental H+/heme a, CuA ratios measured upon stepwise reduction/oxidation of the metals were reproduced by mathematical simulation based on the coupling of oxido−reduction of both heme a and CuA to pK shifts of common acid−base groups. The vectorial nature of the proton−electron coupling at heme a/CuA was analyzed by measuring pH changes in the external bulk phase associated with oxido−reduction of these redox centers in the CO-inhibited oxidase reconstituted in liposomes. The results show that the proton release associated with the oxidation of heme a and CuA takes place in the external aqueous phase. Protons taken up by the oxidase upon rereduction of the centers derive, on the other hand, from the inner space. These results provide evidence supporting the view that cooperative proton−electron coupling at heme a/CuA is involved in the proton pump of the oxidase
Effect of Antimycin on the kinetics of reduction of b and c1 cytochromes in single turnover of the mitochondrial b-c1 complex
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Proton transfer reactions associated with the reaction of the fully reduced, purifierd cytochome c oxidase with molecular oxygen and ferrycianide
No full textA study is presented on proton transfer associated with the reaction of the fully reduced, purified bovine heart cytochrome c oxidase with molecular oxygen or ferricyanide. The proton consumption associated with aerobic oxidation of the four metal centers changed significantly with pH going from ≈3.0 H+/COX at pH 6.2−6.3 to ≈1.2 H+/COX at pH 8.0−8.5. Rereduction of the metal centers was associated with further proton uptake which increased with pH from ≈1.0 H+/COX at pH 6.2−6.3 to ≈2.8 H+/COX at pH 8.0−8.5. Anaerobic oxidation of the four metal centers by ferricyanide resulted in the net release of 1.3−1.6 H+/COX in the pH range 6.2−8.2, which were taken up by the enzyme on rereduction of the metal centers. The proton transfer elicited by ferricyanide represents the net result of deprotonation/protonation reactions linked to anaerobic oxidoreduction of the metal centers. Correction for the ferricyanide-induced pH changes of the proton uptake observed in the oxidation and rereduction phase of the reaction of the reduced oxidase with oxygen gave a measure of the proton consumption in the reduction of O2 to 2H2O. The results show that the expected stoichiometric proton consumption of 4H+ in the reduction of O2 to 2H2O is differently associated, depending on the actual pH, with the oxidation and reduction phase of COX. Two H+/COX are initially taken up in the reduction of O2 to two OH- groups bound to the binuclear Fe a3−CuB center. At acidic pHs the third and fourth protons are also taken up in the oxidative phase with formation of 2H2O. At alkaline pHs the third and fourth protons are taken up with formation of 2H2O only upon rereduction of COX
- …
