Quantitation of Plastoquinone and Functional Electron Carriers in the Photosystem II Reaction Center Complex

Abstract

A few plastoquinone (PQ) molecules, which are bound to the PS I1 reaction center complex, play roles as electron carriers of PS 11. Two electron acceptors, Q_A and Q_B, and secondary electron donor, Z which is regarded to give rise to an EPR signal IIf (IIvf) when oxidized, are assumed to be PQ (1–3). Chemical species responsible for the dark-stable EPR signal I1 (11s) is also expected to be identical with that for signal IIf (IIvf). However, the estimated amount of PQ associated with the complex is usually lower than that of the electron carriers. in addition, there remains controversy about the amount of PQ in the complex (3–5). in the present work, the contents of PQ and functional electron carriers were quantitatively analyzed for the samples extracted with organic solvents to identify the chemical entity of the electron carriers in PS II.