R is driven by two massive intrinsic protein complexes, photosystem I (PSI) and photosystem II (PSII), embedded in the thylakoid membrane. Each PS possesses a number of cofactors, such as quinones (benzoquinone or naphthoquinone derivatives), that are essential for electron transfer. Plastoquinone (PQ) is often a benzoquinone derivative located in PSII (with two binding web sites, QA and QB) and within the PQ pool. PQ is doubly reduced into plastoquinol (PQH2) at the QB site and diffuses inside the membrane to join the PQ pool so allowing the reduction of cytochrome b6f complex (cyt b6f) (Rochaix, 2002). In contrast, naphthoquinone derivatives participate in electron transfer inside PSI. PSI is composed of two core subunits, PsaA and PsaB, containing 11 transmembrane domains and forming the heterodimeric reaction center that coordinates the cofactors essential for electron transfer (Rochaix, 2002). The major PSI electron donor is usually a dimer of chlorophyll a (P700) located on the luminal side from the membrane. Electron transfer from P700 to ferredoxin occurs by way of chlorophyll A0, naphthoquinone A1 and 3 iron ulfur centers [4FeS], denoted FX, FA and FB.MCP-1/CCL2 Protein Storage & Stability Two naphthoquinones are present per P700 and permit electron transfer from A0 to FX by two branches (A and B) (Joliot and Joliot, 1999; GuergovaKuras et al., 2001). To date three types of 2-methyl-1,4naphthoquinone derivatives, also known as vitamin K, have already been identified in diverse oxygenic photosynthetic organisms.SAA1 Protein Storage & Stability They share the same naphthalene nucleus but differ within the prenyl side-chain attached at position 3: menaquinone-4 (vitamin K2) found in bacteria, diatoms and2016 The Authors. 141 The Plant Journal published by Society for Experimental Biology and John Wiley Sons Ltd. This is an open access article under the terms in the Inventive Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, supplied the original perform is properly cited, the use is non-commercial and no modifications or adaptations are made.142 Barbara Emonds-Alt et al. primitive red algae (Yoshida et al., 2003; Ikeda et al., 2008) includes a fully unsaturated C20 isoprenoid side-chain; phylloquinone (PhQ; vitamin K1) located in most cyanobacteria, green algae and land plants, features a phytyl side-chain (partially saturated C20 prenyl); though 50 -monohydroxyphylloquinone (OH-PhQ) is located in Euglena gracilis and in some cyanobacteria like Synechococcus elongatus (Law et al.PMID:24670464 , 1973; Omata and Murata, 1984). Some species, for example the green microalga Chlamydomonas reinhardtii, possess two types of naphthoquinones: PhQ and OH-PhQ (Ozawa et al., 2012). In C. reinhardtii, PhQ and OH-PhQ account for 10 and 90 with the total naphthoquinone content, respectively. Both are functional and contribute to photosynthetic electron transfer (Ozawa et al., 2012). More than the previous decade the conversion of chorismate to menaquinone has been characterized in detail in bacteria (Meganathan, 2001; Jiang et al., 2007, 2008; Chen et al., 2013). Because the various varieties of naphthoquinones are structurally equivalent, a lot of the components from the PhQ biosynthesis pathway inside the cyanobacterium Synechocystis sp. PCC 6803 have been identified by looking the cyanobacterial genome employing bacterial genes as queries. In Synechocystis, nine enzymes, characterized by reverse genetics, catalyze the same methods as these needed for synthesis of menaquinone: MenF (isochorismate synthase), MenD [2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene1-ca.