A mechanism stabilizing a long-lived charge-separated state of photosynthetic reaction centers frozen under intense illumination
It is experimentally shown that slow chilling of photosynthetic reaction centers from purple bacteria Rhodobacter sphaeroides to <230 K under intense illumination leads to appearance of long-lived chargeseparated states (P+Q −A ). This longevity implies that the recombination is blocked or the charge-separated state is stabilized. The longevity effect is caused by structural relaxation of reaction centers to a new equilibrium state that diminishes the free energy difference of recombination. The possible mechanism of such relaxation involves orientation of the polar water molecules in the semiquinone local electrostatic field. Detailed analysis of the longevity effect has been carried out, and its outcome supports the idea that many electron transfer reactions in biological systems are non-equilibrium.