Rapid electron transfer reactions associated with oxygen evolution in photosystem II preparations from spinach andPhormidium laminosum

We have measured the nanosecond kinetics of Chl‐a+IIreduction in oxygen‐evolving detergent preparations of PS II from the cyanobacteriumPhormidium laminosumand from higher plants (spinach) at 824 and 680 nm. Compared to earlier studies at 680 nm with higher plant material, we obtained an improved signal: noise ratio for measurements on a ns to ms time scale. The kinetics of Chl‐a+IIreduction in the ns range are consistent in the two preparations and are comparable to other studies of higher plant and cyanobacterial material. The ns kinetics are tightly connected to the ability for O2evolution. Analysis of the μs kinetics indicates three phases: (a) the slow phase (t½~ 150 μs in spinach and ~ 500 μs inPhormidium) reflects the back reaction between Chl‐a+IIand Q−; (b) the phase witht½5–10 μs is probably due to a donor which is not connected to an intact water oxidation system; (c) the intermediate μs component (t½30–40 μs) may be related to water oxidation.