The Cytochrome b 6 f Complex: A Regulatory Hub Controlling Electron Flow and the Dynamics of Photosynthesis?

2016 ◽  
pp. 437-452
Author(s):  
Giovanni Finazzi ◽  
Jun Minagawa ◽  
Giles N. Johnson
Keyword(s):  
Cytochrome B ◽  
Electron Flow

Heat-stress stimulation of electron flow in a photosystem I submembrane fraction

1990 ◽  
Vol 68 (7-8) ◽  
pp. 999-1004 ◽  
Author(s):  
Natalie Boucher ◽  
Johanne Harnois ◽  
Robert Carpentier
Keyword(s):  
Heat Stress ◽  
Cytochrome B ◽  
Electron Donor ◽  
Photosystem I ◽  
Conformational Changes ◽  
Electron Flow ◽  
Primary Electron ◽  
Primary Electron Donor ◽  
Terminal Electron Acceptor ◽  
Stimulation Of

Oxygen uptake using methyl viologen as the terminal electron acceptor was recorded in digitonin-derived photosystem I submembrane fractions incubated at either 25 or 50 °C. A two- to four-fold heat-stress stimulation of electron flow was detected at 50 °C when reduced 2,6-dichlorophenol-indophenol was used as the primary electron donor. However, no stimulation was seen with N,N,N′,N′ -tetramethylphenylenediamine as the donor. The stimulation was enhanced by specific cations (Mg2+, Na+, K+), but not by Mn2 or Ca2+. The enhancement obtained with Mg2+ could be eliminated by incubating for a prolonged period. It is proposed that the observed heat-stress stimulation is due to a conformational change at the level of the cytochrome b6–f complex. This change increased the affinity of the protein complex for 2,6-dichlorophenol-indophenol at its oxidation sites. The involvement of a conformational modification is demonstrated by the absence of heat-stress stimulation in submembrane fractions immobilized in an albumin–glutaraldehyde cross-linked matrix.Key words: electron transport, photosystem I, heat stress, cytochrome b6–f complex, conformational changes, electron donor.

Histidyl Residues Mediate Electron Transport in Plant Mitochondria

1989 ◽  
Vol 44 (5-6) ◽  
pp. 537-542
Author(s):  
Jaspreet Arora ◽  
P. V. Sane
Keyword(s):  
Electron Transport ◽  
Chemical Modification ◽  
Cytochrome B ◽  
Time Course ◽  
Electron Flow ◽  
Plant Mitochondria ◽  
Oxygen Electrode ◽  
Potato Tubers ◽  
Mitochondrial Membranes ◽  
Maximum Inhibition

Abstract Plant The effect of chemical modification of histidyl residues using diethyl pyrocarbonate (DEP) on plant mitochondrial electron transport was studied. Mitochondrial membranes from potato tubers were isolated and electron flow from NADH to oxygen, NADH to ferricyanide and ascorbate to oxygen were monitored in pro», nee and/or absence of DEP. Measurements were made at various concentrations of DEP and at different pHs either by using an oxygen electrode or spectro-photometrically. The results show that DEP inhibits flow of electrons from NADH to oxygen, however partial electron transport from NADH to ferricyanide and ascorbate to oxygen was unaffected. Maximum inhibition was observed at pH 6.5. The time course of the DEP action revealed a biphasic nature of inhibition. Effects on the levels of reduction of cytochromes b and c by DEP during electron transport indicated that histidyl residues may be present before or at cytochrome b , which are being modified.

scholarly journals Chloroplast cytochrome b-563, hydrophobic environment and lack of direct reaction with ferredoxin

1979 ◽  
Vol 184 (1) ◽  
pp. 39-44 ◽  
Author(s):  
R P Cox
Keyword(s):  
Cytochrome B ◽  
External Medium ◽  
Electron Flow ◽  
Electron Donors ◽  
Direct Reaction ◽  
Measurable Effect ◽  
Hydrophobic Barrier ◽  
Measurable Rate

1. The reaction of electron donors with cytochrome b-563 in chloroplasts was studied by investigating their effects on the rate of its reduction in the presence of dithionite, which reacts only slowly with the cytochrome. The relative effects of 9,10-anthraquinone and 9,10-anthraquinone 2-sulphonate in the presence of dithionite suggested that the site of attack of redox reagents was protected behind a hydrophobic barrier from the external medium. 2. Ferredoxin had no measurable effect on the rate of reduction of the cytochrome in the presence of dithionite. 3. The reduction of pigment P700 in the dark after illumination in the presence of the inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea was stimulated by a combination of NADPH and ferredoxin, although NADPH alone had little effect. The same combination was unable to reduce cytochrome b-563 at a measurable rate. 4. It is concluded that the cytochrome is unlikely to be part of a linear pathway of electron flow between ferredoxin and pigment P700.

scholarly journals Detection of cytochrome b+50 in membranes of Rhodospirillum rubrum isolated from aerobically and phototrophically grown cells

1980 ◽  
Vol 186 (2) ◽  
pp. 453-459 ◽  
Author(s):  
R A Niederman ◽  
C N Hunter ◽  
D E Mallon ◽  
O T Jones
Keyword(s):  
Cytochrome B ◽  
Rhodospirillum Rubrum ◽  
Electron Flow ◽  
Computer Assisted ◽  
Difference Spectra ◽  
Reduction Potentials ◽  
Oxidation Reduction ◽  
Assisted Analysis ◽  
Electron Equivalent ◽  
Three Components

1. Dark equilibrium potentiometric titrations were conducted on membranes purified from Rhodospirillum rubrum in an effort to identify b-type cytochrome components reported in other Rhodospirillaceae. In preparations from aerobically grown cells virtually devoid of bacteriochlorophyll a, three components were observed at 560-540 nm. Their oxidation-reduction midpoint potentials assigned by computer-assisted analysis were +195, +50 and −110 mV at pH 7.0; each of these fitted closely to theoretical single-electron equivalent curves. 2. In chromatophores from phototrophically grown carotenoidless mutant G-9, three components were also observed with E0' +190, +50 and −90mV. 3. The alpha-band of the +50mV component exhibited an absorption maximum near 560nm in difference spectra obtained at fixed oxidation-reduction potentials. 4. This component could be demonstrated most readily in purified membrane preparations and may have been obscured in previous studies by residual cytochrome c'. 5. This is the first definitive report of cytochrome b+50 in membranes from Rs. rubrum and aligns this bacterium with other Rhodospirillaceae in which this component functions in light-driven cyclic electron flow.

scholarly journals Stimulation of the respiratory chain of rat liver mitochondria between cytochrome c1 and cytochrome c by glucagon treatment of rats

1978 ◽  
Vol 172 (3) ◽  
pp. 399-405 ◽  
Author(s):  
Andrew P. Halestrap
Keyword(s):  
Cytochrome C ◽  
Cytochrome B ◽  
Respiratory Chain ◽  
Redox State ◽  
Electron Flow ◽  
Rat Liver Mitochondria ◽  
O2 Uptake ◽  
Pyruvate Metabolism ◽  
Cytochromes C ◽  
Cytochrome C1

Mitochondria from glucagon-treated rats oxidize succinate, but not ascorbate plus tetramethylphenylenediamine, faster in the uncoupled state than do control mitochondria. The rate of O2 uptake in the presence of both substrates is equal to the sum of the rates of the O2 uptake in the presence of either substrate alone. It is concluded that the mitochondrial respiratory chain is limited at some point between cytochromes b and c and that this step is regulated by glucagon. Measurement of the cytochrome spectra under uncoupled conditions in the presence of succinate and rotenone demonstrates a crossover between cytochromes c and c1 when control mitochondria are compared with those from glucagon-treated rats, cytochrome c being more oxidized and cytochrome c1 more reduced in control mitochondria. Under conditions where pyruvate metabolism is studied the control mitochondria are generally more oxidized than those from glucagon-treated rats, the redox state of cytochrome b-566 correlating with the rate of pyruvate metabolism in sucrose medium. However, when the redox state of the mitochondria is taken into account, a crossover between cytochromes c and c1 is again apparent. The spectra of the b cytochromes are complex, but cytochrome b-562 appears to become more reduced relative to cytochrome b-566 in mitochondria from glucagon-treated rats than in control mitochondria. This can be explained by the existence of a more alkaline matrix in glucagon-treated rats, the redox potential for cytochrome b being pH-sensitive. It is concluded that glucagon stimulates electron flow between cytochromes c1 and c. The physiological significance of these findings is discussed.

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