Removal of the PsaF Polypeptide Biases Electron Transfer in Favor of the PsaB Branch of Cofactors in Triton X‐100 Photosystem I Complexes from Synechococcus sp. PCC 7002^†

Abstract

Continuous wave (CW) and transient electron paramagnetic resonance studies have implied that when PsaF is removed genetically, the double reduction of A 1A is facile, the lifetime of A 1A-is shorter and the ratio of fast to slow kinetic phases increases in PS I complexes isolated with Triton X-100 (Van

Structure of a photosystem I-ferredoxin complex from a marine cyanobacterium provides insights into far-red light photoacclimation

“…We cannot be certain how the environment of A 1A changes as a result of the loss of these structural features, but such substantial changes so close to A 1A could result in the formation of a water channel as proposed ( 48 ), especially near the stromal soluble domains of PsaF2 and PsaJ2. The absence of PsaF also resulted in a blue shift in the fluorescence emission maximum and decrease in the long wavelength fluorescence emission at 77 K ( 49 ). When present, the Chls in sites A1 and A2 appear to form a Chl dimer that could contribute to longer wavelength fluorescence emission.…”

Transient EPR: using spin polarization in sequential radical pairs to study electron transfer in photosynthesis

“…Studies involving various isolation procedures (Setif and Brettel 1993) show that the ratio of the two phases in spinach preparations depends on the detergent used and the amount of fast phase is particularly large when Triton X-100 is used. The fact that this effect is also observed in cyanobacterial PS I when PsaF subunit is removed by deletion mutation (van der Est et al 2004;Agalarov et al 2008) suggests that it is also associated with the loss of psaF in spinach preparations. A comparison of the kinetic traces from two samples with differing amounts of the fast component is shown in Fig.…”

“…This result was explained as due to a change in the relative use of the two branches in the absence of the H-bond in one of them. The loss of this H-bond has also been postulated as being responsible for the changes in the relative amplitude of the two phases, when the PsaF subunit is missing and harsh detergents are used to isolate PS I (Agalarov et al 2008). The observation that B-branch mutations can cause changes in either the lifetimes or relative amplitudes of the two kinetic phases suggests that it should be possible to observe the TREPR spectrum of the P 700 ?…”

Introduction to the Symposium‐in‐Print on Photosynthesis

“…Agalarov et al . (9), using the results from both continuous wave and pump‐probe optical spectroscopy, have developed a unified hypothesis that accounted for the long‐recognized but puzzling bias of electron transfer in favor of the PsaB branch of cofactors in Photosystem II. Santabarbara et al .…”

“…Changes both in signal amplitude and signal lifetime in wild-type and mutant systems provide useful information about electron transport pathways. Agalarov et al (9), using the results from both continuous wave and pump-probe optical spectroscopy, have developed a unified hypothesis that accounted for the long-recognized but puzzling bias of electron transfer in favor of the PsaB branch of cofactors in Photosystem II. Santabarbara et al (10) also used pump-probe optical spectroscopy on wild-type and mutant C. reinhardtii cells, in their case to investigate electron-transfer reactions within the Photosystem I reaction center.…”