Temperature dependence of the formation of the g ∼ 5 EPR signal in the oxygen evolving complex of photosystem II

The temperature dependence of the formation of the g similar to 5 S-2 state electron paramagnetic resonance (EPR) signal in photosystem II (PSII) was investigated. The g similar to 5 signal was produced at an illumination above 200 K. The half inhibition temperature of the formation of the g similar to 5 EPR signal was approximately 215 K. The half inhibition temperature is close to that of the transition from the S-2 state-to-S-3 state in the untreated PSII, and not to that of the transition from S-1 state -to-S-2 state in the untreated PSII. The upshift of the half inhibition temperature of the transition from the S-1 state-to-S-2 state (g similar to 5) reflects the structural change upon transition from the S-1 state to the S-2 state. The activation energy of the g similar to 5 state formation was estimated as 40.7 +/- 4.4 kJ/mol, which is comparable to the reported activation energy for the S-2 formation in the untreated PSII. The activation enthalpy and entropy were estimated to be 39.0 +/- 4.4 kJ/mol and - 103 +/- 19 J/mol K at 210 K, respectively. Based on these parameters, the formation process of the g similar to 5 state is discussed in this study.

Automated summary

The temperature dependence of the formation of the g similar to 5 S-2 state electron paramagnetic resonance (EPR) signal in photosystem II (PSII) was investigated. It was found that the g similar to 5 signal can be produced at an illumination above 200 K, and its formation is half inhibited at approximately 215 K. The study also estimated the activation energy, enthalpy, and entropy of the g similar to 5 state formation.