Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.9.3.1 (cytochrome oxidase)
8,822 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The q+/2e stoichiometries (number of charges translocated per electron pair transferred) of cytochrome oxidase and the cytochrome bc1 complex in rat liver mitochondria were determined at a range of membrane potentials up to 180 mV. The method used was similar to the one used in the preceding paper by us in this journal to determine the q+/O stoichiometry of the mitochondrial electron transport chain from succinate to oxygen. The measured q+/2e stoichiometry of cytochrome oxidase was 3.5 positive charges per O atom reduced at low membrane potential (120 mV) and it decreased to about 1.5 at high membrane potential (180 mV). The measured q+/2e stoichiometry of the cytochrome bc1 complex was between 1 and 1.25 positive charges ejected per electron pair and did not change significantly as delta psi was varied from 85 mV to 157 mV. The sum of the q+/2e stoichiometries of cytochrome oxidase and the cytochrome bc1 complex determined separately was similar to their value determined together for electron transport from succinate to oxygen over the range of membrane potentials studied. The most probable interpretation of these results is that the stoichiometry of the cytochrome bc1 complex is invariant over a range of membrane potentials and that the q+/2e stoichiometry of cytochrome oxidase decreases from 4 at low membrane potential to 2 at high membrane potential.
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PMID:The stoichiometry of charge translocation by cytochrome oxidase and the cytochrome bc1 complex of mitochondria at high membrane potential. 283 96

The three coupling segments of the respiratory chain of bovine heart mitochondria were examined individually by steady-state kinetic methods to determine whether or not freely diffusible intermediates occur between the energy-yielding and energy-consuming steps involved in the oxidative phosphorylation of extramitochondrial ADP. The principal method employed was the dual inhibitor technique, for which an appropriate model is provided. The results indicate that in accordance with the chemiosmotic theory the intermediate reactants that link the energy-yielding rotenone-sensitive (Site 1), cytochrome bc1 (Site 2), and cytochrome aa3 (Site 3) reactions of the respiratory chain to the energy-consuming ATP synthetase, AdN transport, and Pi transport reactions are freely diffusible (delocalized). Site 2 was found to differ from the others in regard to the mechanism by which the energy-linked respiratory chain reaction is controlled by the energy-consuming steps. Whereas the Site 1 and Site 3 respiratory chain reactions are controlled primarily by the thermodynamic mechanism of reaction reversal, the Site 2 respiratory reaction is controlled primarily by a kinetic mechanism in which an intermediate that links it to the energy-consuming steps inhibits it allosterically. From the effects of nigericin and valinomycin the allosteric intermediate appears to be the electrical component of the protonmotive force.
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PMID:Steady-state kinetics of the overall oxidative phosphorylation reaction in heart mitochondria. Evidence for linkage of the energy-yielding and energy-consuming steps by freely diffusible intermediates and for an allosteric mechanism of respiratory control at coupling site 2. 286 Jan 3

Several inner membrane proteins from rat liver mitochondria have been translated for the first time in rabbit reticulocyte lysates. These include the Rieske iron-sulfur protein, cytochrome c1 and core protein I of the cytochrome bc1 complex, the alpha and beta subunits of F1 ATPase, and subunit IV of cytochrome oxidase. All were translated from free polysomes as larger-molecular-mass precursors, and were processed to their mature forms by isolated liver mitochondria or by the isolated mitochondrial matrix fraction. In vitro processing, catalyzed by the isolated matrix fraction, is inhibited by rhodamine 6G. The latter is a fluorescent probe, which accumulates specifically in mitochondria of whole cells and which is used extensively to visualize mitochondrial morphology. The concentration of rhodamine 6G required for inhibition in vitro is similar to that of o-phenanthroline. Rhodamine 6G inhibits matrix-catalyzed processing of all precursors tested, indicating that the mechanism of inhibition is common for a variety of functionally unrelated precursors. The novel action of rhodamine 6G reported here can form the basis for its inhibition of precursor processing in intact hepatoma cells [Kolarov, J. & Nelson, B.D. (1984) Eur. J. Biochem. 144, 387-392].
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PMID:Rhodamine 6G inhibits the matrix-catalyzed processing of precursors of rat-liver mitochondrial proteins. 286 95

Distinct fluorophores have been conjugated to antibodies for cytochrome bc1 complex and cytochrome oxidase, two integral electron transferring proteins in the mitochondrial inner membrane. Addition of these fluorescent antibodies to preparations of mitochondrial inner membranes followed by appropriate secondary antibodies causes distinct and independent aggregation of the two cytochrome proteins. These results reveal that both cytochrome bc1 complex and cytochrome oxidase diffuse laterally in the membrane plane independent of one another consistent with the random collision model for electron transport in the mitochondrial inner membrane.
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PMID:Independent lateral diffusion of cytochrome bc1 complex and cytochrome oxidase in the mitochondrial inner membrane. 299 81

Complex III (cytochrome bc1 particle; ubiquinol:ferricytochrome c oxidoreductase, EC 1.10.22) was purified from beef heart mitochondria by affinity chromatography. Phospholipids were depleted by washing the particle with detergent while it still was on the affinity column. The particle first was mixed with an excess of cytochrome c in 1.5% cholate (wt/vol); slow removal of the detergent from the mixture was achieved by dialysis. Freezing of the mixture resulted in crystallization of the cytochrome bc1 particle in the form of a 1:2 complex with cytochrome c. The chemical composition and spectrophotometric properties of the crystal are described. The same crystallization maneuver used in the case of cytochrome oxidase has been demonstrated to be effective in crystallizing the middle part of the mitochondrial electron-transfer chain.
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PMID:Crystallization of the middle part of the mitochondrial electron transfer chain: cytochrome bc1-cytochrome c complex. 625 56

Cytochrome oxidase was incorporated into lipid vesicles composed of phosphatidylethanolamine-phosphatidylcholine-cardiolipin. Large proteoliposomes of 1,000-15,000 A diameter were prepared by calcium-induced fusion of small vesicles. Rotational diffusion of cytochrome oxidase was measured by detecting the decay of the absorption anisotropy, r(t), after photolysis of the heme a3.CO complex by a vertically polarized laser flash. Because of the large size of the proteoliposomes, there was no contribution of vesicle-tumbling to r(t) over the experimental time range of 5 ms for samples in 60% sucrose. Analysis of r(t) curves was based on a "rotation-about-membrane normal" model. The measurements were used to investigate intermolecular interactions between cytochrome oxidases and between cytochrome oxidase and cytochrome bc1 complex co-reconstituted in the above lipid vesicles. In vesicles of a high lipid to protein ratio (congruent to 27), nearly all cytochrome oxidase molecules are rotating with an approximate rotational relaxation time, phi 1, on the order of 500 microseconds. In contrast, about 20% of cytochrome oxidase is immobile in vesicles with a relatively low lipid to protein ratio (congruent to 5), although phi 1 of the mobile population remains about 500 microseconds. In contrast, about 20% of cytochrome oxidase is immobile in vesicles with a relatively low lipid to protein ratio (congruent to 5), although phi 1 of the mobile population remains about 500 microseconds. The immobilized fraction is presumably due to nonspecific self-aggregation of cytochrome oxidase. The presence of cytochrome bc1 complex does not change r(t) curves significantly, either in the presence or absence of cytochrome c. Previously, we have observed the co-existence of mobile and immobile populations of cytochrome oxidase in bovine heart and rat heart mitochondria (Kawato, S., Sigel, E., Carafoli, E., and Cherry, R. J. (1980) J. Biol. Chem. 255, 5508-5510). The present results suggest that the immobile population of about one-half of cytochrome oxidase could be simply due to nonspecific protein aggregation resulting from the high concentration of enzymes in the inner mitochondrial membrane (lipid to protein ratio, less than or equal to 0.5). We also conclude that there is no specific interaction between cytochrome oxidase and cytochrome bc1 complex in the above large lipid vesicles. A lateral collision-controlled model for electron transfer from cytochrome bc1 complex to cytochrome oxidase through cytochrome c is discussed based on the above results.
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PMID:Rotation of cytochrome oxidase in phospholipid vesicles. Investigations of interactions between cytochrome oxidases and between cytochrome oxidase and cytochrome bc1 complex. 626 51

We report here that N,N'-dicyclohexylcarbodiimide (DCCD) decreases the H/2e stoichiometry of the cytochrome bc1 complex from 3.8 +/- 0.2 (10) to 2.1 +/- 0.1 (8) but has only a minimal effect on the H/2e ratio of cytochrome oxidase under the relatively mild conditions used. The effect on the bc1 complex cannot be explained by uncoupling, by inhibition of electron transport or by selective mitochondrial damage. We conclude that DCCD is an inhibitor of proton translocation within the bc1 complex. There are three possible explanations of this effect: (a) DCCD could alter the pathway of electron flow, (b) DCCD could prevent one of the proton translocation reactions but not electron transport, (c) DCCD could prevent the conduction of the translocated proton to the external phase.
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PMID:Chemical modification of the mitochondrial bc1 complex by N,N'-dicyclohexylcarbodiimide inhibits proton translocation. 630 80

A screen has been performed of possible inhibitors of the ubiquinol oxidase of higher plant mitochondria by assaying their effects on cyanide-insensitive NADH oxidase of mitochondria of Arum maculatum. A number of compounds which have powerful inhibitory effects have been identified. Potent inhibition was found with compounds related to the previously described n-propyl gallate, but with the n-propyl sidechain replaced with alkyl chains of greater hydrophobicity. Titration of a range of partial reactions showed that the inhibitors act specifically on the ubiquinol oxidase. The concentrations of inhibitor required are dependent on the respiratory substrate and on the amount of mitochondria used in the assay. Octyl gallate also proved to be a potent inhibitor of the ubiquinol oxidase in tobacco cell suspensions. A second class of compounds which strongly inhibit cyanide-insensitive NADH oxidation is aurachin C and its analogues. Compounds related to aurachin D are much less effective. Titrations of a range of partial reactions indicate that inhibition is caused by a direct action on the ubiquinol oxidase. However, both types of aurachins also act strongly at the Qi site of the cytochrome bc1 complex, as already known to be the case in other systems, and so they are of more limited value for studies of the ubiquinol oxidase. Titration of the oxidation of NADH via the ubiquinol oxidase in a purified mitochondrial fraction from the spadices of Arum maculatum with octyl gallate gave a half-maximal effect at a concentration of around 6 nM when the protein concentration was 14 micrograms ml-1. A similar titre was obtained with a decyl derivative of aurachin C. This allowed us to estimate an upper limit for the concentration of ubiquinol oxidase in these mitochondria of 0.72 +/- 0.15 nmol mg-1 protein, or a ratio of ubiquinol oxidase/cytochrome oxidase of about 15 +/- 7:1. The measurements also provide a minimal turnover number for the ubiquinol oxidase of 186 +/- 42 electrons.s-1. Titration of the ubiquinol oxidase in soybean cotyledon mitochondria with these compounds gave the concentration of inhibitor required to elicit 50% of the maximum observed effect (I50) values about one order of magnitude higher than those found with Arum mitochondria, and again the values depended on the respiratory substrate. An explanation for the variation in I50 values may be found in terms of differences in oxidase concentrations in the different mitochondrial membranes and in the differences in rate-controlling steps with substrates of different activities.
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PMID:New inhibitors of the ubiquinol oxidase of higher plant mitochondria. 758 98

Unlike mitochondria, many bacteria use a large repertoire of c-type cytochromes in different branches of their electron transport system. Among the many cytochromes c present in the soil bacterium Paracoccus denitrificans, a membrane-bound cytochrome (c552) has been suggested to mediate the electron transport between the cytochrome bc1 complex and cytochrome-c oxidase [Berry, E. A. & Trumpower, B. L. (1985) J. Biol. Chem. 260, 2458-2467]. We have purified this cytochrome from cytoplasmic membranes, and cloned and sequenced its gene, cycM. Sequence analysis reveals that, while its C-terminal portion is highly similar to type-I cytochromes c, its N-terminal part contains a hydrophobic segment providing membrane attachment. In addition, we present immunological evidence for its functional role in respiration.
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PMID:Purification of Paracoccus denitrificans cytochrome c552 and sequence analysis of the gene. 762 79

A cytochrome-c (cyt c) oxidase supercomplex consisting of 7-8 subunits and possessing a mass of 358-425 kDa was purified from Bradyrhizobium japonicum bacteroid membranes. At least two subunits possess c-type heme as a prosthetic group. One of the c-heme-containing components was detected in bacteroid membranes, but not in free-living cells. The complex also contains b-heme, and both b-type and c-type heme proteins were spectrophotometrically shown to form complexes with carbon monoxide. A CO difference spectrum showed an absorption minimum (trough) at 551.7 nm, possibly corresponding to a previously described cyt c-552 in bacteroid membranes. 1 mM quinacrine (Atebrin) had no effect on O2 uptake by the cytochrome-c oxidase complex, but 10 mM inhibited O2 uptake by 90%. Cytochromes b and c1 of the cytochrome bc1 respiratory complex were identified as two of the components of the bacteroid complex based upon immunoreaction with antibodies against these two proteins from B. japonicum. The oxidase complex oxidized exogenously added horse heart ferrocytochrome c concomitant with the uptake of oxygen. It could also oxidize the artificial electron donor N,N,N',N'-tetramethyl-p-phenylenediamine in the absence of added cytochrome c. Oxygen uptake activity was completely inhibited by 10 microM NaCN and 38% by 0.1 microM NaCN. The oxidase complex was not able to oxidize a ubiquinol homolog possessing a single isoprenoid unit side chain. Solubilization of bacteroid membranes in the presence of 1.0 mM EDTA resulted in complete loss of cytochrome-c oxidase activity. Leghemoglobin deoxygenation data indicated that the oxidase complex can efficiently function at free oxygen concentrations well below 1.0 microM, even though attempts to determine the oxidase's specific affinity oxygen were unsuccessful due to the formation of oxidized leghemoglobin derivatives.
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PMID:Purification and characterization of an O2-utilizing cytochrome-c oxidase complex from Bradyrhizobium japonicum bacteroid membranes. 839 77


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