scholarly journals The properties of the primary electron acceptor in the Photosystem I reaction centre of spinach chloroplasts and its interaction with P700 and the bound ferredoxin in various oxidation-reduction states

1976 ◽  
Vol 158 (1) ◽  
pp. 71-77 ◽  
Author(s):  
M C W Evans ◽  
C K Sihra ◽  
R Cammack
Keyword(s):  
Low Temperature ◽  
Photosystem I ◽  
Electron Acceptor ◽  
Low Temperatures ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Sodium Dithionite ◽  
Primary Electron ◽  
Resonance Spectroscopy ◽  
Reaction Centre ◽  
Primary Electron Acceptor

The properties of the component ‘X’ identified as the primary electron acceptor of Photosystem I in spinach was investigated by electron-paramagnetic-resonance spectroscopy and the complete spectrum obtained for the first time. Component ‘X’ has gx = 1.78, gy = 1.88 and gz = 2.08; it can be observed only at very low temperatures (8-13K) and high microwave powers. Component X was identified in Photosystem I particles prepared with the French press or with Triton X-100. In samples reduced with ascorbate, illumination at low temperatures results in the photo-oxidation of P700 and reduction of a bound iron-sulphur protein; this is irreversible at low temperature. In samples in which the iron-sulphur proteins are reduced by sodium dithionite, illumination at low temperature results in the oxidation of P700 and the reduction of component ‘X’; this is reversible at low temperature. The light-induced P700 signal is the same size with either ascorbate or dithionite as reducing agent, showing that all of the P700 involved in reduction of bound ferredoxin also functions in the reduction of component ‘X’.

scholarly journals Quantitative electron-paramagnetic-resonance measurements of the electron-transfer components of the photosystem-I reaction centre. The reaction-centre chlorophyll (P700), the primary electron acceptor X and bound iron-sulphur centre A

1978 ◽  
Vol 170 (2) ◽  
pp. 373-378 ◽  
Author(s):  
P Heathcote ◽  
D L Williams-Smith ◽  
M C W Evans
Keyword(s):  
Free Radical ◽  
Electron Transport ◽  
Photosystem I ◽  
Electron Acceptor ◽  
Line Shape ◽  
Primary Electron ◽  
Reaction Centre ◽  
Electron Spins ◽  
Average Value ◽  
Primary Electron Acceptor

An e.p.r. spectrum of the reduced form of the electron-transport component (X), thought to be the primary electron acceptor of Photosystem I, was obtained. By using line-shape simulations of this component and the free-radical e.p.r. signal I of the oxidized reaction-centre chlorophyll (P700), it was possible to determine the ratio of the number of electron spins to which these signals correspond in Photosystem-I particles under a variety of conditions. On illumination at cryogenic temperatures of Photosystem-I preparations, in which both bound iron-sulphur centres A and B were reduced, the measured ratio of free radical to component X varied between 1.04 and 2.23, with an average value of 1.54 +/- 0.18 where a Gaussian line-shape is assumed for the component-X signal in the simulation. The error in this measurement is estimated to be up to 50%. In a similar way component X and centre A of the bound iron-sulphur protein were quantified, the ratio between these two components varying between 1.26 and 0.61 with an average value of 0.75 +/- 0.06. These results indicate that the quantitative relationship, in terms of net electron spins, between centre A, component X and P700 is of the order to be expected if component X is indeed the primary electron acceptor in Photosystem I and a component of the photosynthetic electron-transport chain.

scholarly journals The detection and characterization by electron-paramagnetic-resonance spectroscopy of iron–sulphur proteins and other electron-transport components in chromatophores from the purple bacterium Chromatium

1974 ◽  
Vol 138 (2) ◽  
pp. 177-183 ◽  
Author(s):  
Michael C. W. Evans ◽  
Anne V. Lord ◽  
Stuart G. Reeves
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Electron Transport ◽  
Electron Acceptor ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Primary Electron ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Midpoint Potential ◽  
Primary Electron Acceptor ◽  
Electron Paramagnetic

Low-temperature e.p.r. (electron-paramagnetic-resonance) spectroscopy was used to detect electron-transport components in Chromatium chromatophores with e.p.r. signals in the g=2.00 region. High-potential iron protein (Em8.0=+325mV, where Em8.0 is the midpoint potential at pH8) and a second component (g=1.90, Em8.0=+285mV) are oxidized in illuminated chromatophores. Two iron–sulphur proteins (g=1.94) with Em8.0=−290mV and Em8.0=−50mV are present. One (Em8.0=−50mV) is reduced on illumination. A component (g=1.82) with Em8.0=−135mV is photoreduced at 10°K. The midpoint potential of this component is altered by o-phenanthroline and pH. The properties of this component suggest that it is the primary electron acceptor of a photochemical system. Another component (g=1.98) also has some of the properties of a primary electron acceptor, but its function cannot be completely defined. These results show that iron–sulphur proteins are present in the electron-transport system of Chromatium and indicate their role in electron transport.

The site of electron transport inhibition by bentazon (3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide) in isolated chloroplasts

1982 ◽  
Vol 60 (4) ◽  
pp. 409-412 ◽  
Author(s):  
Rungsit Suwanketnikom ◽  
Kriton K. Hatzios ◽  
Donald Penner ◽  
Duncan Bell
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Electron Acceptor ◽  
Photosynthetic Electron Transport ◽  
Primary Electron ◽  
Photochemical Reactions ◽  
Spinacea Oleracea ◽  
Primary Electron Acceptor ◽  
Isolated Chloroplasts

The effect of bentazon (3-isopropyl-1H-2,1,3-benzathiadiazin-(4)3H-one 2,2-dioxide) on various photochemical reactions of isolated spinach (Spinacea oleracea L.) chloroplasts was studied at concentrations 0, 5, 15, 45, and 135 μM. Bentazon at a concentration of 135 μM strongly inhibited uncoupled electron transport from water to ferricyanide or to methylviologen with inhibition percentages greater than 90%. Photosystem II mediated electron transport from water to oxidized diaminodurene, with 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) blocking photosystem I, was also strongly inhibited by bentazon at 135 μM but less with lower concentrations of bentazon. Photosystem I mediated transfer of electrons from diaminodurene to methylviologen, with 3,4-dichlorophenyl-1,1-dimethylurea (DCMU) blocking photosystem II, was not inhibited by bentazon at any concentration examined. Transfer of electrons from catechol to methylviologen in hydroxylamine-treated chloroplasts was inhibited by bentazon, and the inhibition percentages were again concentration dependent. The data indicate that the site of bentazon inhibition of the photosynthetic electron transport is at the reducing side of photosystem II, between the primary electron acceptor Q and plastoquinone.

Primary electron acceptor complex of photosystem I in spinach chloroplasts

Nature ◽  
1975 ◽  
Vol 256 (5519) ◽  
pp. 668-670 ◽  
Author(s):  
M. C. W. EVANS ◽  
C. K. SIHRA ◽  
J. R. BOLTON ◽  
R. CAMMACK
Keyword(s):  
Photosystem I ◽  
Electron Acceptor ◽  
Primary Electron ◽  
Acceptor Complex ◽  
Spinach Chloroplasts ◽  
Primary Electron Acceptor
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