Oxygenic Photosynthesis Photosystem

In plants, algae and cyanobacteria the light-induced charge separation of photosynthesis occurs in 2 large membrane proteins, called photosystem (PS) I and II. PS I catalyzes the ET from plastocyanin (or cytochrome c6) on the luminal side to ferrodoxin (or flavodoxin) on the stromal side of the membrane (for review see reference 177). PS I from the cyanobacterium Thermo(Y13)synechococcus (T.) elongatus was crystallized and an X-ray crystallographic structure at 2.5 A resolution has recently been obtained.18,178 Very recently, the structure from plant PS I has also been reported with a resolution of 4.4 A.179 

The protein complex of T. elongatus consists of 12 subunits that contain 96 Chi a and 22 carotenoid molecules, 3 [4Fe4S] centres and 2 phylloquinone (vitamin K,) molecules (for molecular structures see Fig. 2). The cofactors of the ET chain are arranged in two branches as pairs of molecules related by a pseudo-C2 axis. After light excitation an electron is donated from the primary donor P700, a pair of chlorophylls, to monomeric chlorophyll a (acceptor A0), phylloquinone (A() and the 3 iron-sulfur centres (F , Oa and t B). It has been controversially discussed in the literature whether both highly symmetric pigment branches are 

In this series the review by Mdbius103 covered the literature on PS I up to early 1994. Since that time a very large number of paper ( 200) appeared in this narrow field that cannot be covered here in detail. The work on the FeS centres in PS I and related structures has been reviewed regularly by Hiittermann and Kappl.181 184 The interested reader is also referred to a special issue of Biochimica et Biophysica Acta (Bioenergetics) entirely devoted to PS I27 that contains six reviews in which EPR techniques are in the focus of research87,185 1851 In the following the key results obtained from EPR techniques applied to PS I will be highlighted. 

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Whereas the 2[4Fe-4S] ferredoxin may have been replaced by the [2Fe-2S] ferredoxins in oxygenic photosynthesis, another 2[4Fe-4S] protein, the so-called FA/FB-binding subunit (see Fig. 1), appears to be common to all RCI-type photosystems. 

Figure 10.3 Z-scheme of oxygenic photosynthesis in green algae and cyanobacteria, showing links to hydrogenase. Q (plastoquinone) and X (an iron-sulfur cluster) are electron acceptors from photosystems II and I, respectively.The two hydrogenases shown are the NADP-dependent bidirectional hydrogenase and a ferredoxin-dependent enzyme.

Triazines inhibit photosynthesis in all organisms with oxygen-evolving photosystems. They block photosynthetic electron transport by displacing plastoquinone from a specific-binding site on the D1 protein subunit of photosystem II (PS II). This mode of action is shared with several structurally different groups of other herbicides. The elucidation of the mechanism of the inhibitory action is followed in this review. 

Satoh, K. (1996). Introduction to photosystem II reaction center Isolation and biochemical and biophysical characterization. In D.R. Qrt and C.F. Yocum, eds., Oxygenic Photosynthesis. Boston Kluwer, pp. 193-212. 

The oxidation of water by Photosystem II in oxygenic photosynthesis is an energetically and mechanistically challenging process, in which... 

Diner, B.A., and Rappaport, F. 2002. Structure, dynamics, and energetics of the primary photochemistry of Photosystem II of oxygenic photosynthesis. Annu. Rev. Plant Biol 53 551-580. 

Nugent, J.H.A. 1996. Oxygenic photosynthesis Electron transfer in Photosystem I and Photo-system II. Eur. J. Biochem. 237 519-531. 

FTR plays the central role in light regulation of the activity of enzymes involved in oxygenic photosynthesis. The light signal is converted into reducing equivalents in the form of reduced 2Fe Fd by photosystem I and FTR catalyzes the reduction of disulfides in thioredoxin (Trx) / and m using the... 

Two Photosystems Generate a Proton Gradient and NADPH in Oxygenic Photosynthesis. 

The reaction centre pigments in the cyanobacteria (blue-green algae), the prochlorophytes and all photosynthetic eukaryotes are chlorophylls. There are two types of reaction centre in organisms carrying out oxygenic photosynthesis, namely photosystems I and The primary electron... 

Lavergne J and Briantais J-M. (1996). Photosystem-II heterogeneity. In Ort DR and Yocum CF (Eds), Oxygenic photosynthesis The Light Reactions, pp. 265-287. Kluwer Academic Publishers,... 

R1. BA Diner and GT Babcock (1996) Structure, dynamics, and energy conversion efficiency in photosystem II. In DR Ort and CF Yocum (eds) Oxygenic Photosynthesis The Light Reactions, pp 213-247. Kluwer R2. BA Diner, V Petrouleas and JJ Wendoloski (1991) The iron-quinone-acceptor complex of photosystem II. Phyiol Plant 81 423-436... 

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