An electron paramagnetic resonance investigation of the electron transfer reactions in the chlorophyll d containing photosystem I of Acaryochloris marina

Electron paramagnetic resonance (EPR) spectroscopy reveals functional and structural similarities between the reaction centres of the chlorophyll d-binding photosystem I (PS I) and chlorophyll a-binding PS I. Continuous wave EPR spectrometry at 12 K identifies iron–sulphur centres as terminal electron acceptors of chlorophyll d  -binding PS I. A transient light-induced electron spin echo (ESE) signal indicates the presence of a quinone as the secondary electron acceptor (Q) between P740+ and the iron–sulphur centres. The distance between P740+ and Q− was estimated within point-dipole approximation as 25.23 ± 0.05 Å, by the analysis of the electron spin echo envelope modulation.