Fig. 7: The PSI of C. velia as an enzymatic machine for oxygen photoreduction. | Nature Communications

Fig. 7: The PSI of C. velia as an enzymatic machine for oxygen photoreduction.

From: The cryo-EM structure of Photosystem I from Chromera velia with a bound superoxide dismutase heterodimer

Fig. 7

PSI and PSII are co-localized or organized as a supercomplex in C. velia and oxygen therefore concentrates around PSI. Due to the weaker affinity of ferredoxin for PSI, oxygen is readily reduced to superoxide (O2−) and immediately dismutated into peroxide and oxygen either by PSI-attached FeSOD or by soluble MnSOD. The oxygen molecules from the dismutase half-reaction can undergo another round of reduction by PSI. The peroxide is finally converted back into water by the abundant thiol peroxiredoxins (PRX). As the reducing substrate of PRX are in most cases thioredoxins, this reaction serves as another sink for electrons in the chloroplast (see “Discussion”).

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