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Research Fellows Directory

Alfred Rutherford

Professor Alfred Rutherford EMBO member

Research Fellow


Imperial College London

Research summary

Photosystem II (PSII) uses light to drive water oxidation and quinone reduction at the start of the photosynthetic electron transfer chain. Photosynthetic electron transfer produces the NADPH and ATP that drive CO2 fixation. PSII is easily photodamaged and can act as a source of reactive oxygen species; it is therefore highly regulated and protected. We have recently discovered evidence that CO2, through its equilibrium with bicarbonate, can control PSII activity and protect it against photodamage by redox tuning its first quinone cofactor, QA. We found that i) when PSII lacks bicarbonate, the electrochemical potential of QA up-shifts to a lower energy value and ii) when QA is reduced, forming QA-, it promotes the dissociation bicarbonate. The tuning of QA’s potential allows the high energy states generated by light to relax without generating toxic excited state oxygen even when the energy cannot be used to do photosynthesis. These results indicate the existence of an electron-sink (CO2) to electron-source (PSII) regulatory mechanism: when CO2 is limiting the electron transfer chain becomes over-reduced in the light, leading to QA- formation in PSII, this favours bicarbonate release, which tunes the potential of QA, diminishing enzyme activity and protecting PSII from photodamage. When CO2 levels rise these changes are reversed and normal service from PSII is resumed. The existence of this unsuspected regulation mechanism provides new lines of research at a molecular level and in vivo and these are potentially relevant across all types of oxygenic organisms. Regulatory mechanisms are central to photosynthesis research, with a great deal of research attention being paid to them. This focus on regulation is justified since understanding regulatory mechanisms in detail could allow them to be controlled or modified in order to optimise growth to specific conditions. This could translate into new ways to improve the efficiency of photosynthesis and crop yields

Interests and expertise (Subject groups)

Grants awarded

Biological and artificial water photolysis

Scheme: Wolfson Research Merit Awards

Dates: Apr 2011 - Mar 2016

Value: £100,000