Interaction of membrane‐embedded cytochrome b ‐complexes with quinols: Classical Q‐cycle and murburn model

2022 ◽  
Author(s):  
Kelath Murali Manoj ◽  
Daniel Andrew Gideon ◽  
Laurent Jaeken
Keyword(s):  
Cytochrome B ◽  
Q Cycle

The Kinetics of Reactions in and Near the Cytochrome b/f Complex of Chloroplasts. II. Cytochrome b-563 Reduction

1989 ◽  
Vol 16 (4) ◽  
pp. 353 ◽  
Author(s):  
AB Hope ◽  
J Liggins ◽  
DB Matthews
Keyword(s):  
Electron Transfer ◽  
Cytochrome B ◽  
Rate Constant ◽  
Apparent Rate Constant ◽  
Rate Limiting Step ◽  
Q Cycle ◽  
Proton Transfers ◽  
Wide Range ◽  
Dimethyl Urea ◽  
Rate Limiting

The reduction of cytochrome b-563 was measured following flash-induced electron transfer from duroquinol to methyl viologen, in the presence of 3,(3,4-dichlorophenyl)-1,1-dimethyl urea and 1 �M nonactin or 1 �M valinomycin (plus 10 mM K+). The apparent rate constant of this reduction (nonactin present) increased from about 100 s-1 to 460 s-1 as the external concentration of duroquinol was varied from 0.01 to 0.5 mM. The corresponding maximum extent of reduction of cytochrome b-563 varied from 0.13 to 0.27 molecules per b/f complex. Rate constants in the presence of valinomycin were lower at all concentrations of duroquinol by a factor of about 1.5. The mean enthalpy of activation calculated from Arrhenius plots of apparent rate constant for cytochrome b-563 reduction was 60 kJ mol-1, for temperature variation between 23 and 4°C. The above, and further data in oxidising conditions, and with added 2-n-nonyl-4-hydroxyquinoline N-oxide, together with data on proton deposition, were compared with the predictions of a kinetic model. In this model, flash-generated oxidised plastocyanin oxidised Rieske centres during random diffusion, and plastoquinol reduced the Rieske centres and cytochrome b-563 sequentially; subsequent electron and proton transfers followed those in a Q-cycle. Many observations were predicted by the model, in which the rate-limiting step was the first electron transfer from plastoquinol to the Rieske centre, subsequent steps being much faster. The rate and extent of reduction of cytochrome b-563 were fully consistent with a reaction between it and a radical form of plastoquinone formed after oxidation of the latter by Rieske centres (referred to as 'oxidant-induced reduction'), under a wide range of conditions.

The Kinetics of Oxidation of Cytochrome B are in Agreement with the Q-Cycle Hypothesis

1987 ◽  
pp. 517-522 ◽  
Author(s):  
S. de Vries ◽  
A. N. van Hoek ◽  
A. ten Bookum ◽  
J. A. Berden
Keyword(s):  
Cytochrome B ◽  
Kinetics Of Oxidation ◽  
Q Cycle ◽  
Kinetics Of

The Slow Phase of the Electrochromic Shift in Relation to the Q-Cycle in Thylakoids

1987 ◽  
Vol 14 (1) ◽  
pp. 29 ◽  
Author(s):  
AB Hope ◽  
DB Matthews
Keyword(s):  
Electron Transport ◽  
Cytochrome B ◽  
Methyl Viologen ◽  
Slow Phase ◽  
Half Time ◽  
Electrochromic Shift ◽  
Q Cycle ◽  
Reducing Conditions ◽  
Low Concentrations ◽  
Micromolar Range

The electrochromic signal in oxidising conditions with whole-chain electron transport from water to ferricyanide or methyl viologen was compared with that under reducing conditions with electron transport from duroquinol to methyl viologen. Under oxidising conditions, in a train of flashes at 10 Hz, the slow phase in the growth of the electrochromic signal was not apparent after a few flashes whilst under reducing conditions it persisted. The slow phase of the electrochromic signal was also examined particularly under conditions favouring the operation of an apparent Q-cycle, namely oxidising conditions plus the addition of low concentrations of valinomycin and flashes given at 5-10 Hz. The slow phase was retained in the presence of valinomycin at flash rates up to 10 Hz and its decay was accelerated. The half-time for the slow phase was 18-20 ms (whole-chain), or 3-5 ms (reducing conditions, duroquinol/methyl viologen). There was a lag of 3 ms before the rise of the slow phase with ferricyanide. The onset was accelerated by valinomycin under oxidising conditions. The slow phase was sharply inhibited by 2-n-heptyl- and 2-n-nonyl-4-hydroxyquinoline N-oxide (HQNO and NQNO) to at least half its maximum extent by 0.1 �M (HQNO) or 0.05 �M (NQNO); further inhibition took place in the micromolar range. The slow phase is discussed in terms of probable electrogenic events in the cytochrome b/f complexes and their kinetics. We support the hypothesis that its basic cause is the transverse, intramembrane passage of electrons and show that this passage is controlled by the prevailing intramembrane potential difference, an estimated 85-140 mV sufficing for half inhibition of the slow phase.

Some Observations on Intra-Mitochondrial Crystals

1977 ◽  
Vol 35 ◽  
pp. 406-407
Author(s):  
J. A. Clarke ◽  
D. N. Landon ◽  
P. R. Ward
Keyword(s):  
Cytochrome B ◽  
Mitochondrial Myopathy ◽  
Crystallographic Analysis ◽  
Mitochondrial Membranes ◽  
Electron Microscopes ◽  
Muscle Biopsies

Intra-mitochondrial crystals have been noted in muscle biopsies from patients in a wide variety of diseased states. As far as we are aware, none of these crystals have been subjected to detailed crystallographic analysis. Recently, similar crystals were observed in a biopsy from a patient with a mitochondrial myopathy, characterised by a deficiency in reducible cytochrome b (Morgan-Hughes, J. A., Darveniza, P., Kahn, S. N., Landon, D. N., Sherratt, R. M., Land, J. M. and Clark, J. B., 1977, Brain, In Press). Aldehyde-fixed, osmicated resin imbedded material was examined using Siemens, JEOL and Phillips electron microscopes with goniometer specimen stages. The crystals generally lay between the outer and inner mitochondrial membranes and measured 1 - 3 μm in length and 0.1 - 0.3 μm in width. Characteristically, these crystals revealed specific periodicities.

scholarly journals A juvenile Tristan albatross (Diomedea dabbenena) on land at the Crozet Islands

Polar Biology ◽  
2020 ◽  
Author(s):  
Alexander L. Bond ◽  
Christopher Taylor ◽  
David Kinchin-Smith ◽  
Derren Fox ◽  
Emma Witcutt ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Cytochrome B ◽  
Adult Male ◽  
Mitochondrial Gene ◽  
Small Population ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
Tristan Da Cunha ◽  
Gough Island ◽  
Dispersal Events

AbstractAlbatrosses and other seabirds are generally highly philopatric, returning to natal colonies when they achieve breeding age. This is not universal, however, and cases of extraordinary vagrancy are rare. The Tristan Albatross (Diomedea dabbenena) breeds on Gough Island in the South Atlantic Ocean, with a small population on Inaccessible Island, Tristan da Cunha, ca 380 km away. In 2015, we observed an adult male albatross in Gonydale, Gough Island, which had been ringed on Ile de la Possession, Crozet Islands in 2009 when it was assumed to be an immature Wandering Albatross (D. exulans). We sequenced 1109 bp of the cytochrome b mitochondrial gene from this bird, and confirmed it to be a Tristan Albatross, meaning its presence on Crozet 6 years previous, and nearly 5000 km away, was a case of prospecting behaviour in a heterospecific colony. Given the challenges in identifying immature Diomedea albatrosses, such dispersal events may be more common than thought previously.

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