PHOTOCHEMICAL PROPERTIES OF THE PHEOPHYTIN PRIMARY ELECTRON ACCEPTOR IN PHOTOSYSTEM II

Abstract

This chapter discusses the photochemical properties of the pheophytin primary electron acceptor in photosystem II (PS-II). Plant photosynthesis begins with the absorption of photons by chloroplasts followed by charge separation and stabilization, thus, converting photonic energy to chemical energy. In a experiment described in the chapter, chemical analysis showed that the PS-II fragments contain two nonheme Fe-atoms per reaction center. The iron content and electron paramagnetic resonance (EPR) doublet were unaffected when the PS-II fragments were treated with 0.5 M LiClO4, but the Fe-content decreased to 0.6 per reaction center and the EPR doublet almost completely disappeared when the fragments were treated with 0.55 M LiClO4 and 2.5 mM o-phenanthroline. Properties of the EPR doublet in PS II show a remarkable similarity in the chemical make-up of PS II and the photosynthetic bacteria, and are consistent with the idea that an exchange interaction between reduced pheophytin and the singly reduced PQ− –Fe2+ complex produces the EPR doublet signal.