Unidirectional photodamage of pheophytin in photosynthesis

Abstract

The primary reactions in photosynthesis take place in the reaction centers surrounded by light harvesting complexes (Blankenship, 2002; Diner and Rappaport, 2002; Frank and Brudvig, 2004). There are two types of photosynthetic reaction centers. The type I reaction center has iron-sulfur cluster as stable electron acceptor, such as photosystem I complexes, green bacterial and heliobacterial reaction centers, and the type II uses quinone as stable electron acceptor including photosystem II and purple bacterial reaction centers. The electron transfer in type II reaction center in unidirectional via the L-subunit of the reaction centers (Maroti et al., 1985; Hoerber et al., 1986; Martin et al., 1986; Michel-Beyerle et al., 1988). However, the electron transfer in the type I reaction center is different from that in the type II centers, which is bidirectionational (Guergova-Kuras et al., 2001; Li et al., 2006). The three dimensional structures of both types of reaction centers were determined at atomic resolution (Jordan et al., 2001; Ferreira et al., 2004; Loll et al., 2005; Amunts et al., 2007; Umena et al., 2011). The electron transfer pathways in both types of reaction centers are well established (Van Grondelle, 1985; Schatz et al., 1988; Fleming and van Grondelle, 1997; Dekker and Van Grondelle, 2000; Gobets and van Grondelle, 2001; Seibert and Wasielewski, 2003; Van Grondelle and Novoderezhkin, 2006). The primary electron donor in the reaction centers is a pair of chlorophyll molecules, and pheophytin is the primary electron acceptor (Klimov et al., 1977; Holzwarth et al., 2006).