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Microalgae II: Cell Structure, Nutrition and Metabolism
Published in Arun Kumar, Jay Shankar Singh, Microalgae in Waste Water Remediation, 2021
Photosystem II is a membrane-embedded-protein-complex that comprises of more than 20 subunits and a molecular mass of about 300 kDa. It has a reaction center, inner light-harvesting antennae and oxygen-evolving complex. The PS II reaction center comprises of proteins D1 and D2; and two subunits cyt b559 i.e., a and b subunits. The D1 and D2 proteins hold all essential prosthetic groups that are the integral part of the primary electron donor, P680, tyrosine Z, pheophytin and the quinone acceptors, QA and QB; and are also required for the charge separation and its stabilization. The inner core antennae contains the intrinsic Chl a-proteins i.e., CP43 and CP47 that are located on the opposite sides of D1-D2 reaction center (Hankamer et al. 2001); and is responsible for the transfer of excitation energy from the outer antennae to the reaction center.
Abiotic Stress in Plants
Published in Hasanuzzaman Mirza, Nahar Kamrun, Fujita Masayuki, Oku Hirosuke, Tofazzal M. Islam, Approaches for Enhancing Abiotic Stress Tolerance in Plants, 2019
Ashutosh K. Pandey, Annesha Ghosh, Kshama Rai, Adeeb Fatima, Madhoolika Agrawal, S.B. Agrawal
At the physiological level, the photosynthetic rate varies with climatic conditions, plant species, cultivars, photosynthetically active radiation (PAR) and UV-B. Earlier reports have clearly presented the damage induced with the exposure of UV-B radiation on the photosynthetic machinery, thylakoid membrane, light harvesting complexes and both the photosystems (I and II), causing deleterious impact on the assimilative performance of the plants. Photosystem II is one of the most sensitive components of photophosphorylation and is responsible for the splitting of water in the presence of light (Correia et al., 1999; Kakani et al., 2003; Savitch et al., 2001). Correia et al. (1999) have reported significant reduction of photosynthesis by 25–46% in wheat crop under elevated doses of UV-B compared to ambient conditions. Photosynthesis in plants is also regulated by an important factor, stomatal conductance; several studies have demonstrated that elevated UV-B leads to the reduction of stomatal conductance and, hence, is responsible for CO2 assimilation to some extent (Zhao et al., 2003). Jansen summarized that stomata exposed to elevated UV-B lose their ability to readjust and regulate their original functioning, leading to the partial opening of stomata.
Natural Organic Photosynthetic Solar Energy Transduction
Published in Sun Sam-Shajing, Sariciftci Niyazi Serdar, Organic Photovoltaics, 2017
The electrons extracted from water are donated to Photosystem II, and after a second light-driven electron transfer step by Photosystem I [8], eventually reduce an intermediate electron acceptor, the oxidized form of nicotinamide adenine dinucleotide phosphate (NADP+). Protons are also transported across the membrane and into the thylakoid lumen during the process of the noncyclic electron transfer, creating a pH difference, which contributes to the proton motive force. The energy in this proton motive force is used to make ATP. The NADPH and ATP that are formed in the light-driven steps of photosynthesis are used to fix CO2 to form sugars and other organic products that give energy for metablolism and growth of the organism. Excess stored energy is available to us in the form of food, fiber, and biomass.
Vibrational spectroscopy of free di-manganese oxide cluster complexes with di-hydrogen
Published in Molecular Physics, 2023
Sandra M. Lang, Thorsten M. Bernhardt, Joost M. Bakker, Bokwon Yoon, Uzi Landman
The direct conversion of solar energy into storable and renewable fuels is one of the main challenges of modern catalysis research. Inspired by natural photosynthesis, sun-light driven water oxidation followed by the hydrogen evolution reaction (HER, i.e. proton reduction) has attracted much interest and huge research efforts have been invested in this direction during the past decade (see e.g. Ref. [1–7] for recent review articles). Among the various processes involved in artificial photosynthesis the catalysis of the energy demanding water oxidation (reaction 1) represents one of the main challenges (see e.g. Ref. [1,6–10]). In nature, this half-reaction (i.e. the oxidative part of the water plus carbon dioxide redox reaction) is catalysed by the oxygen evolving complex (OEC), which is embedded in the protein structure of photosystem II (PS II). X-ray diffraction studies revealed that the OEC consists of an inorganic CaMn4O5 cluster surrounded by a network of amino acid residues and water molecules [11,12].
Theory of chemical bonds in metalloenzymes XXII: a concerted bond-switching mechanism for the oxygen–oxygen bond formation coupled with one electron transfer for water oxidation in the oxygen-evolving complex of photosystem II
Published in Molecular Physics, 2019
K. Yamaguchi, M. Shoji, H. Isobe, K. Miyagawa, K. Nakatani
Photosystem II (PSII) is a multi-subunit protein complex embedded in the thylakoid membrane of green plants, algae and cyanobacteria [1,2]. PSII is the engine for all aerobic life on our planet [3–5]. It produces reducing equivalents for making carbohydrates and provides us molecular oxygen as by product as shown in Equation (1). Past decades, a number of experimental studies were performed for elucidation of structure and reactivity of the calcium-doped four-manganese cluster (CaMn4) involved in oxygen-evolving complex (OEC) of PSII [3–6]. Extended X-ray absorption fine structure (EXAFS) experiments [3,7–12] elucidated the geometrical parameters of the catalytic CaMn4Ox cluster in OEC of PSII. X-ray diffraction (XRD) experiments [13–24] were performed for determination of its three-dimensional (3D) structure. Electron paramagnetic resonance (EPR) spectroscopy [25–31] was applied to elucidate electronic and spin states of the CaMn4Ox cluster. Available EXAFS, XRD and EPR experimental results revealed that the CaMn4Ox cluster in OEC of PSII exhibits multi-faced characteristics depending on the environmental effects.
Theory of chemical bonds in metalloenzymes XXI. Possible mechanisms of water oxidation in oxygen evolving complex of photosystem II
Published in Molecular Physics, 2018
Kizashi Yamaguchi, Mitsuo Shoji, Hiroshi Isobe, Shusuke Yamanaka, Takashi Kawakami, Satoru Yamada, Michio Katouda, Takahito Nakajima
Photosystem II (PSII) is a multi-subunit protein complex embedded in the thylakoid membrane of green plants, algae and cyanobacteria [1,2]. PSII is the engine for all aerobic life on our planet [3–5]. Water oxidation in PSII produces reducing equivalents for making carbohydrates and provides us molecular oxygen as by product. Past decades a number of experimental studies have been performed for elucidation of geometrical, electronic and spin structures of the calcium-doped four-manganese cluster (CaMn4) involved in oxygen evolving complex (OEC) of PSII [3–6]. Extended X-ray absorption fine structure (EXAFS) experiments [3,7–12] were performed for elucidation of the geometrical parameters of the catalytic CaMn4Ox cluster in OEC of PSII. X-ray diffraction (XRD) experiments [13–24] were also conducted to determine its 3D structure. Electron paramagnetic resonance (EPR) spectroscopy [25–31] was applied to elucidate electronic and spin states of the CaMn4Ox cluster. Available EXAFS, XRD and EPR experimental results revealed that the CaMn4Ox cluster in OEC of PSII exhibits multi-faced characteristics depending on the environmental effects and experimental conditions.