Multiple pathways of charge recombination revealed by the temperature dependence of electron transfer kinetics in cyanobacterial photosystem I

Publication date: Available online 25 June 2019Source: Biochimica et Biophysica Acta (BBA) - BioenergeticsAuthor(s): Georgy Milanovsky, Oksana Gopta, Anastasia Petrova, Mahir Mamedov, Michael Gorka, Dmitry Cherepanov, John H. Golbeck, Alexey SemenovAbstractThe kinetics of charge recombination in Photosystem I P700-FA/FB complexes and P700-FX cores lacking the terminal iron‑sulfur clusters were studied over a temperatures range of 310 K to 4.2 K. Analysis of the charge recombination kinetics in this temperature range allowed the assignment of backward electron transfer from the different electron acceptors to P700+. The kinetic and thermodynamic parameters of these recombination reactions were determined. The kinetics of all electron transfer reactions were activation-less below 170 K, the glass transition temperature of the water-glycerol solution. Above this temperature, recombination from [FA/FB]− in P700-FA/FB complexes was found to proceed along two pathways with different activation energies (Ea). The charge recombination via A1A has an Ea of ~290 meV and is dominant at temperatures above ~280 K, whereas the direct recombination from FX− has an Ea of 22 meV and is prevalent in the 200 K to 270 K temperature range. Charge recombination from the FX cluster becomes highly heterogeneous at temperatures below 200 K. The conformational mobility of Photosystem I was studied by molecular dynamics simulations. The FX cluster was found to ‘swing’ by ~30...

Source: Biochimica et Biophysica Acta (BBA) Bioenergetics - June 25, 2019 Category: Biochemistry Source Type: research