An investigation of water splitting in the Kok scheme of photosynthetic oxygen evolution

The involvement of OH bond breaking in the 4 dark reactions of the Kok scheme of photosynthetic oxygen evolution was investigated using Chlorella and spinach chloroplasts. When the photosynthetic material was suspended in a ²H₂O based medium, the reaction rates in all 4 cases were only slightly reduced as compared to the rates observed in an H₂O based medium. This was evidence that these rate processes were probably not limited by the breaking of an OH bond. Observations were also made on the yields of O₂ from dark adapted Chlorella subjected to a sequence of brief saturating light flashes. The oscillating flash yield sequence observed with algae suspended in ²H₂O showed greater damping of the oscillations than when the algae were suspended in H₂O. A computer fit of the Kok model to these results revealed a slightly higher proportion of misses, (i.e. absorbed quanta that do not drive photochemistry) in the ²H₂O case.