Electron transfer through the quinone acceptor complex of Photosystem II in bicarbonate-depleted spinach thylakoid membranes as a function of actinic flash number and frequency

Chloroplast thylakoid membranes depleted of bicarbonate exhibit a slowed oxidation of the primary quinone acceptor (Qᴀ) by the secondary quinone acceptor (Qв) of photosystem II. The kinetics of these slowed reactions have been followed by using short xenon flashes of light both to excite photosystem II and to probe the redox state of Qᴀ. Thylakoids incubated with formate but not depleted of bicarbonate showed the same pattern of slowed reaction kinetics of the quinone acceptors as seen in bicarbonate-depleted| thylakoids. This led us to conclude that there was a simple competition between bicarbonate and formate at this site; however, steady-state electron transfer measured with an oxygen electrode showed that although the bicarbonate- depleted thylakoids were indeed inhibited, rates in the formate-incubated thylakoids were only slightly slowed. We suggest that the inhibition seen at the quinone acceptor site of photosystem II depends in a subtle way upon the rate of exchange of bicarbonate and formate at this site.

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A highly resolved, oxygen-evolving photosystem II preparation from spinach thylakoid membranes

FEBS Letters ◽

10.1016/0014-5793(81)80608-4 ◽

1981 ◽

Vol 134 (2) ◽

pp. 231-234 ◽

Cited By ~ 1407

Author(s):

Deborah A. Berthold ◽

Gerald T. Babcock ◽

Charles F. Yocum

Keyword(s):

Photosystem Ii ◽

Thylakoid Membranes ◽

Spinach Thylakoid ◽

Oxygen Evolving

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Electron acceptors of bacterial photosynthetic reaction centers II. H+ binding coupled to secondary electron transfer in the quinone acceptor complex

Biochimica et Biophysica Acta (BBA) - Bioenergetics ◽

10.1016/0005-2728(79)90138-5 ◽

1979 ◽

Vol 548 (2) ◽

pp. 309-327 ◽

Cited By ~ 176

Author(s):

C.A. Wraight

Keyword(s):

Electron Transfer ◽

Secondary Electron ◽

Reaction Centers ◽

Electron Acceptors ◽

Photosynthetic Reaction Centers ◽

Acceptor Complex ◽

Quinone Acceptor

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Bicarbonate Activation of Monomeric Photosystem II-PsbS/Psb27 Complex

10.1101/2022.01.13.476245 ◽

2022 ◽

Author(s):

A. William Rutherford ◽

Andrea Fantuzzi ◽

Dario Piano ◽

Patrycja Haniewicz ◽

Domenica Farci ◽

...

Keyword(s):

Electron Transfer ◽

Photosystem Ii ◽

Water Splitting ◽

Thylakoid Membranes ◽

Protective Mechanism ◽

Slow Electron ◽

Enhanced Fluorescence ◽

Transfer Rates ◽

Redox Tuning ◽

In Transit

In thylakoid membranes, Photosystem II monomers from the stromal lamellae contain the subunits PsbS and Psb27 (PSIIm-S/27), while Photosystem II monomers from granal regions (PSIIm) lack these subunits. Here, we have isolated and characterised these two types of Photosystem II complexes. The PSIIm-S/27 showed enhanced fluorescence, the near-absence of oxygen evolution, as well as limited and slow electron transfer from QA to QB compared to the near-normal activities in the granal PSIIm. However, when bicarbonate was added to the PSIIm-S/27, water splitting and QA to QB electron transfer rates were comparable to those in granal PSIIm. The findings suggest that the binding of PsbS and/or Psb27 inhibits forward electron transfer and lowers the binding affinity for the bicarbonate. This can be rationalized in terms of the recently discovered photoprotection role played by bicarbonate binding via the redox tuning of the QA/QA?- couple, which controls the charge recombination route, and this limits chlorophyll triplet mediated 1O2 formation (Brinkert K et al. (2016) Proc Natl Acad Sci U S A. 113(43):12144-12149). These findings suggest that PSIIm-S/27 is an intermediate in the assembly of PSII in which PsbS and/or Psb27 restrict PSII activity while in transit, by using a bicarbonate-mediated switch and protective mechanism.

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