Transient electron paramagnetic resonance (TR-EPR) spectra of the electron-hole pair state P700+A0Q K- in photosystem I are numerically calculated. Parameter variation concerns mainly the exchange integral J of the precursor spin pair state P700+A0QK and its lifetime τ. A prominent emissive feature in the high-field region (P 700+ part) of the EPR spectrum turns out to be diminished with increasing lifetime τ of the precursor pair state in the case of positive exchange coupling J > 0 (ferromagnetic type). Correspondingly, the emissive feature becomes more pronounced with increasing lifetime τ in the case of negative exchange coupling J < 0 (antiferromagnetic type). These results can be used to interpret the changes in the pattern observed in TR-EPR spectra comparing wild-type and specific A0 mutants. The central ligating amino acid residue to the A0 chlorophyll cofactor is mutated from native methionine (M) to leucine (L) in either the PsaA or the PsaB branch. Changes are observed only for the A-side mutant: M688L(PsaA). They are consistent with the following parameters in the precursor pair P 700+A0-: J ≈ 0.5 ÷ 1.0 mT and τ = 1.5 ÷ 2 ns (as compared to τ ∼ 0.05 ns in the wild type).
All Science Journal Classification (ASJC) codes
- Atomic and Molecular Physics, and Optics