scholarly journals The pathway of electron flow through ubiquinol:cytochrome c oxidoreductase in the respiratory chain. Evidence from inhibition studies for a modified ‘Q cycle’

1982 ◽  
Vol 204 (1) ◽  
pp. 49-59 ◽  
Author(s):  
A P Halestrap
Keyword(s):  
Mitochondrial Membrane ◽  
Electron Flow ◽  
Reduced Form ◽  
Protonmotive Force ◽  
Reverse Effect ◽  
Aerobic Conditions ◽  
Q Cycle ◽  
Cytochromes C ◽  
Flow Through ◽  
Inhibition Studies

1. Cytochrome spectra of the liver and heart mitochondria incubated under various conditions are presented to compare the effects of antimycin, colletotrichin and 2-heptyl-4-hydroxyquinoline N-oxide (HQNO) additions. 2. Under aerobic conditions, in State 4, in the presence of uncoupler or in the presence of cyanide, all three inhibitors caused oxidation of cytochromes c and c1, but different changes in the spectra of the b cytochromes. Antimycin caused oxidation of a peak at 558 nm and reduction of peaks at 562 nm and 566 nm, whereas colletotrichin caused reduction of peaks at 558 nm and 566 nm and oxidation at 562 nm. HQNO had an effect on the spectra intermediate between those of the two other inhibitors. 3. Under aerobic conditions in the presence of 5 mM-succinate and 5 mM-fumarate, antimycin caused reduction of a peak at 566 nm and oxidation of a peak at 558 nm, whereas colletotrichin had the reverse effect and HQNO caused reduction of a peak at 562 nm. 4. Colletotrichin inhibition of the ADP-stimulated oxidation of glutamate + malate was enhanced by succinate addition and declined again with rotenone addition. Similar but smaller effects were seen with inhibition by antimycin and HQNO. 5. Cytochrome spectra are shown of the effects of ADP and uncoupler addition to stimulate respiration progressively. 6. The results are interpreted in terms of a modified ‘Q cycle’ [Mitchell (1976) J. Theor. Biol. 62, 327-367] in which the three inhibitors are postulated to displace ubiquinone and ubisemiquinone specifically bound to cytochromes b on both sides of the membrane. 7. It is suggested that cytochromes b558 and b566 are the same b cytochrome located on the outer surface of the membrane, but binding ubisemiquinone or colletotrichin and ubiquinone or antimycin respectively. Cytochrome b562 is postulated to be on the inner surface of the mitochondrial membrane and to bind either ubiquinone or ubisemiquinone, HQNO would bind to the reduced form of the cytochrome and colletotrichin to the oxidized form. 8. Sites for the locus of action of glucagon and the protonmotive force on electron flow are suggested.

scholarly journals The nature of the stimulation of the respiratory chain of rat liver mitochondria by glucagon pretreatment of animals

1982 ◽  
Vol 204 (1) ◽  
pp. 37-47 ◽  
Author(s):  
A P Halestrap
Keyword(s):  
Respiratory Chain ◽  
Electron Flow ◽  
Liver Mitochondria ◽  
Complex Iii ◽  
Secondary Site ◽  
Rat Liver Mitochondria ◽  
Succinate Oxidation ◽  
Q Cycle ◽  
Cytochromes C ◽  
Stimulation Of

1. Studies on the cytochrome spectra of liver mitochondria from control and glucagon-treated rats in State 4, State 3 and in the presence of uncoupler are reported. 2. The stimulation of electron flow between cytochromes c1 and c observed previously [Halestrap (1978) Biochem. J. 172, 399-405] was shown to be an artefact of Ca2+-induced swelling of mitochondria. 3. When precautions were taken to prevent such swelling, glucagon treatment was shown to enhance the reduction of cytochromes c, c1 and b558 in both State 3 and uncoupled conditions with either succinate or glutamate + malate as substrate. An increase in the reduction of cytochromes b562 and b566 was also seen in some, but not all, experiments. 4. In State 4 with succinate but not glutamate + malate as substrate, cytochromes c, c1, b558, b562 and b566 showed increased reduction. 5. Glucagon stimulated oxidation of duroquinol and palmitoylcarnitine by intact mitochondria and of NADH by disrupted mitochondria. 6. No effect of glucagon on succinate dehydrogenase activity or the temperature-dependence of succinate oxidation could be detected. 7. Glucagon enhanced the inhibition of the respiratory chain by colletotrichin, but not antimycin or 8-heptyl-4-hydroxyquinoline N-oxide. 8. These results are interpreted in terms of a primary stimulation by glucagon of the ‘Q cycle’ [Mitchell (1976) J. Theor. Biol. 62, 827-367] within Complex III (ubiquinol:cytochrome c oxidoreductase) and a secondary site of action involving stimulation of electron flow into Complex III from the ubiquinone pool. 9. Ageing of mitochondria, hyperosmotic treatment or addition of 20 mM-benzyl alcohol opposed the effects of glucagon treatment on cytochrome spectra and colletotrichin inhibition of respiration. 10. These results support the hypothesis that glucagon exerts its effects on the mitochondria by perturbing the membrane structure.

scholarly journals Reduction of cytochromes by nitrite in electron-transport particles from Nitrobacter winogradskyi: proposal of a mechanism for H+ translocation

1976 ◽  
Vol 156 (3) ◽  
pp. 493-498 ◽  
Author(s):  
J G Cobley
Keyword(s):  
Electron Transport ◽  
Cytochrome C ◽  
Respiratory Chain ◽  
Single Electron ◽  
Reduced Form ◽  
Protonmotive Force ◽  
Carbonyl Cyanide ◽  
Cytochromes C ◽  
Electrical Component ◽  
No2 Oxidation

1. A novel component in the respiratory chain of Nitrobacter winogradskyi was identified. This component absorbs maximally at 552.5 nm when in its reduced form, has an Eo' (pH7.0) value of-110mV and undergoes reduction by a mechanism involving the transfer of a single electron. 2. Degrees of reduction of cytochromes c and a1 in electron-transport (ET) particles were monitored during the course of NO2- oxidation, and the effects of ADP together with Pi, oligomycin and of carbonyl cyanide phenylhydrazone were determined. 3. The influences of ionophorous antibiotics, NH4Cl and cyclohexylamine hydrochloride on the reductions of cytochromes c and a1 by NO2- indicate that the flow of reducing equivalents from cytochrome a1 (+350mV) to cytochrome c (+270mV) is facilitated by deltapsi, the electrical component of the protonmotive force. 4. Cytochromes c and a1 in ET particles are reduced by the non-physiological reductant KBH4 in a manner similar to that observed with the physiological reductant NO2-. 5. To account both for the observed cytochrome reductions and for the translocation of H+ ions which accompanies NO2- oxidation, a mechanism is proposed which involves the transfer of a hydride equivalent (H+ plus 2e) inward across the membrane of the ET particle in response to deltapsi.

scholarly journals The C Termini of Constitutive Nitric-oxide Synthases Control Electron Flow through the Flavin and Heme Domains and Affect Modulation by Calmodulin

2000 ◽  
Vol 275 (38) ◽  
pp. 29225-29232 ◽  
Author(s):  
Linda J. Roman ◽  
Pavel Martásek ◽  
R. Timothy Miller ◽  
Dawn E. Harris ◽  
Melissa A. de la Garza ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Electron Flow ◽  
Nitric Oxide Synthases ◽  
Flow Through

Electron Flow through Geometrical Discontinuity in Coaxial Magnetically Insulated Transmission Lines

2000 ◽  
Vol 39 (Part 1, No. 9A) ◽  
pp. 5280-5286 ◽  
Author(s):  
Kazuki Hiraoka ◽  
Mitsuo Nakajima ◽  
Makoto Shiho ◽  
Kazuhiko Horioka
Keyword(s):  
Transmission Lines ◽  
Electron Flow ◽  
Flow Through ◽  
Geometrical Discontinuity

SINGLE ELECTRON DEVICES

1998 ◽  
Vol 09 (01) ◽  
pp. 165-207 ◽  
Author(s):  
DORAN D. SMITH
Keyword(s):  
Tunnel Junctions ◽  
Electron Flow ◽  
Superconducting Devices ◽  
Time Correlation ◽  
Single Electron ◽  
Net Charge ◽  
Flow Through ◽  
Single Electron Devices ◽  
Electron Devices ◽  
Electron Effects

In the mid 1980s Averin and Likharev predicted that with the use of ultrasmall tunnel junctions a time correlation of electron flow through a junction could be observed, and permit the measurement of the effect of a net charge of less than one electron on the junction. Both effects were soon experimentally verified, and since that time there has been an explosion of work in the filed of single electron devices. This chapter reviews the fundamental concepts behind the operation of such devices. it then describes some of the single electron effects studied in semiconductors. Superconducting devices are then constrasted to the semiconductor and the normal metal single electron devices. The details of some current applications are described, and a thumbnail sketch of current fabrication methods is given.

scholarly journals Correction to Electron Flow through Metalloproteins

2016 ◽  
Vol 116 (14) ◽  
pp. 8313-8313
Author(s):  
Jay R. Winkler ◽  
Harry B. Gray
Keyword(s):  
Electron Flow ◽  
Flow Through

Degradation of the D -l Protein Subunit of Photosystem II in Isolated Thylakoids by UV Light

1990 ◽  
Vol 45 (7-8) ◽  
pp. 765-771 ◽  
Author(s):  
Achim Trebst ◽  
Brigitte Depka
Keyword(s):  
Photosystem Ii ◽  
Uv Light ◽  
Electron Flow ◽  
Protein Subunit ◽  
Aerobic Conditions ◽  
L Protein ◽  
Quinone Binding ◽  
Thylakoid Membrane Proteins ◽  
Specific Degradation

Abstract Thylakoid membranes from spinach were irradiated with UV light of 254 nm. Photosynthetic electron flow driven by photosystem II, but not by photosystem I is fully inactivated in about 2-5 min. Inactivation of electron flow is prevented by inhibitors of the QB site of both the DCMU and of the phenol type. UV light inactivates electron How both under anaerobic and aerobic conditions. This is in contrast to white light where fast inactivation occurs only under anaerobic conditions and where only inhibitors of the DCMU-type protect. Inactivation of electron flow by UV light is followed on a slower time scale by a specific degradation of thylakoid membrane proteins. As shown by immunoblotting the D-1 protein and to a smaller extent also the D-2 protein subunit - that together form the reaction center of photosystem II - are de- graded during UV light irradiation. The disappearance of these proteins occurs only under aerobic conditions. Both types of QB site inhibitors prevent the degradation of the two plasto-quinone-binding proteins. A degradation product of the D-l protein is observed at about 8 kDa size. The results are discussed in their relevance to rapid turnover and photoinhibition in vivo and to the topology of the quinone-binding site in the D-1 and D-2 protein.

scholarly journals The effects of acetaldehyde on nitrogenase, hydrogenase and photosynthesis in the cyanobacterium Anabaena cylindrica

1983 ◽  
Vol 212 (3) ◽  
pp. 755-758 ◽  
Author(s):  
B Slatyer ◽  
A Daday ◽  
G D Smith
Keyword(s):  
Methyl Viologen ◽  
Co2 Fixation ◽  
Electron Flow ◽  
Anabaena Cylindrica ◽  
O2 Uptake ◽  
Irreversible Inhibitor ◽  
Photosynthetic Electron Flow ◽  
Separate Electron ◽  
Cyanobacterium Anabaena ◽  
Flow Through

Acetaldehyde was shown to be an irreversible inhibitor of nitrogenase, hydrogenase, CO2 fixation and growth in the cyanobacterium Anabaena cylindrica, but had no effect on photosynthetic electron flow as measured by Methyl Viologen-dependent O2 uptake. The concentration-dependence of the inhibition of nitrogenase and hydrogenase activities was determined, and it was shown that acetaldehyde inhibition poses problems for anaerobic experiments in which the activities of these enzymes are measured in the presence of the frequently used glucose/glucose oxidase/catalase/ethanol O2 trap. It is suggested that acetaldehyde may find use as an inhibitor in experiments designed to separate electron flow through the photosystems from consequent fixation of CO2 and N2.

Further Studies of Proton Translocations in Chloroplasts After Single-Turnover Flashes. I. Proton Uptake

1983 ◽  
Vol 10 (5) ◽  
pp. 363 ◽  
Author(s):  
AB Hope ◽  
DB Matthews
Keyword(s):  
Ionic Strength ◽  
Electron Flow ◽  
External Solution ◽  
Half Time ◽  
Cycle Model ◽  
Single Turnover ◽  
Q Cycle ◽  
Proton Uptake ◽  
Factor Α ◽  
Light Flashes

Damped, binary oscillations were observed in proton uptake by class C pea chloroplasts given a train of light flashes. The oscillation at pH 7.8 is predictable if the species accepting protons is either the doubly reduced secondary acceptor B�- or a plastoquinone PQ- from the pool, if 0.29 of the secondary acceptor is B- in dark-adapted chloroplasts and if a miss factor α = 0.12 governs the amval of electrons at B or B- after a flash. The rate of proton uptake was measured with varied pH, ionic strength and temperature. The half-time was 95 ms at pH 7.8 and 21°C. Using double flashes separated by variable intervals showed that the species able to accept protons was generated (t½) about 0.8 ms after a flash. The results are consistent with protons from the external solution reacting relatively slowly with univalent anions, which have earlier promptly supplied protons to B2- or PQ2-. Under conditions of cyclic and of non-cyclic electron flow, H+/e- stoichiometries were 1.1 and 1.0 respectively, and so the results do not support a Q-cycle model for pea chloroplasts.

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