title: Direct assignment of vitamin K1 as the secondary acceptor A1 in photosystem I.
abstract: The characteristic electron spin polarized electron paramagnetic resonance (ESP EPR) signal observed in photosystem I (PSI) has been previously assigned to a radical pair composed of the oxidized primary donor and a reduced vitamin K1. Under conditions in which Bottin, H. & Setif, P. [(1991), Biochim. Biophys. Acta 105, 331-336] proposed that A1 is doubly reduced, the ESP EPR signal was not observed. Therefore, the ESP EPR signal can be directly attributed to A-1, and vitamin K1 can be assigned as this PSI acceptor. The ESP EPR signal was partially restored by removal of the chemical reductants.
authors.affiliation: Chemistry Division, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: S W
authors.initials: SW
authors.lastname: Snyder
authors.forename: R R
authors.initials: RR
authors.lastname: Rustandi
authors.forename: J
authors.initials: J
authors.lastname: Biggins
authors.forename: J R
authors.initials: JR
authors.lastname: Norris
authors.forename: M C
authors.initials: MC
authors.lastname: Thurnauer