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Production of Clean Energy from Cyanobacterial Biochemical Products
Published in Stephen A. Roosa, International Solutions to Sustainable Energy, Policies and Applications, 2020
It is known that cyanobacteria possess thylakoid, granum and other pigments, capturing the energy from sunlight using photosynthetic systems (PSII and PSI) to perform photosynthesis [20,21,39,41]. The pigments in PSII (P680) absorb the photons, generating a strong oxidant capable of splitting water into protons (H+), electrons (e) and O2 as shown in Figure 4-5. The electrons or reducing equivalents are transferred through a series of electron carriers and cytochrome complex to PSI. The pigments in PSI (P700) absorb the photons, which further raises the energy level of the electrons to reduce the oxidized ferredoxin (Fd) and/or nicotinamide adenine dinucleotide phosphate (NADP+) into their reduced forms. The proton gradient formed across the cellular (or thylakoid) membrane drives adenosine triphosphate (ATP) production via ATP synthase.
Biochemical Pathways for the Biofuel Production
Published in Debabrata Das, Jhansi L. Varanasi, Fundamentals of Biofuel Production Processes, 2019
Debabrata Das, Jhansi L. Varanasi
In direct biophotolysis, reduced electrons produced by photosynthesis during water splitting are used directly by H2-producing hydrogenase without intermediate CO2 fixation. In this process, the light energy is captured by the photochemical reaction centers PSI and PSII which consist of distinct photochemical reaction centers P700 and P680, respectively (Figure 4.2). These light-harvesting photosystems use the solar energy to split water into hydrogen and oxygen. The electrons generated through this process are channeled towards Ferredoxin (Fd) and further are directly taken up by hydrogenases under suitable conditions (i.e., anaerobic conditions). The major disadvantage of this process is the extreme sensitivity of hydrogenase to oxygen. Hydrogenase gets deactivated at the O2 partial pressure of less than 2% (Singh and Das 2018). Thus, the hydrogen productivity is too low in this process due to the oxygen inhibition. To improve the hydrogen yields, a two-stage direct photolysis is performed under sulfur-deprivation conditions (Das and Veziroglu 2008). In such conditions, the PSII activity (which requires sulphur for its biosynthesis) is partially suppressed and, in turn, lowers the oxygen evolution. This process helps in the development of an anaerobic condition inside the cell and helps the hydrogenases to be active for longer duration of time. The organisms such as Synechocystis sp. (cyanobacteria) and Chlamydomonas reinhardtii (green algae) produce hydrogen through direct photolysis mechanism.
Photosynthesis
Published in Thomas M. Nordlund, Peter M. Hoffmann, Quantitative Understanding of Biosystems, 2019
Thomas M. Nordlund, Peter M. Hoffmann
Where are the absorption bands of P680 and P700 in the spectra of Figure 10.7? If the Z scheme has any hope of being correct, shouldn’t we be able to identify 680- and 700-nm peaks? The answer is “Yes,” and the reason we cannot see such peaks reveals another important and, in retrospect, expected feature of the photosynthetic apparatus. P680 and P700 were identified as chlorophyll-containing “reaction centers” of a photosynthetic unit (PSU) containing 250–300 chlorophylls. If the reaction center chlorophylls comprised only one or two of the chlorophylls, their absorbance would be extremely small. The large majority of the chlorophylls, the ones that produce the green in leaves, are “light-harvesting” or “antenna” chlorophylls—pigments that absorb light and transfer energy to the reaction centers. (The other fact is that Figure 10.7 was assembled from spectra of isolated pigments; it is not the absorption spectrum of an intact leaf or algae suspension.) Such samples indeed show apparent absorption in the 680–700 nm region, but scattered light dominates the absorption. The only way to eliminate such scattering is to disintegrate the cells, which, unfortunately, also destroys reaction center complexes.
Theoretical study on interaction of cytochrome f and plastocyanin complex by a simple coarse-grained model with molecular crowding effect
Published in Molecular Physics, 2018
Satoshi Nakagawa, Isman Kurniawan, Koichi Kodama, Muhammad Saleh Arwansyah, Kazutomo Kawaguchi, Hidemi Nagao
Plastocyanin (Pc) is a small soluble protein and one of type I copper proteins. The structure of Pc by X-ray analysis has been presented by many groups [1–4]. The active site of Pc consists of one copper ion coordinated by two histidines, one cystein in a trigonal planar structure, and variable axial ligands such as the sulfur ion of methionine. Pc has the function of the electron transfer from cytochrome f (Cytf) in cytochrome b6f complex to P700 in photosystem I. The structure of Cytf has been established by C. J. Carrell and coworkers [5]. Cytf is unique among c-type cytochromes in its fold and heme ligation and has the soluble domain in the lumen-side segment. The reduction reaction of Pc is rapid with the complex between the soluble domain in Cytf and soluble Pc. The structure of the short-lived and weak complex between Cytf and Pc has been investigated by some groups [6–9]. Crowley and coworkers [8] have discussed the structure of the Cytf-Pc complex in relation to the hydrophobic interaction. The possible structures of the Cytf-Pc complex in the electron transfer reaction have been also discussed from the viewpoint of the balance between the electrostatic and hydrophobic interactions by I. Diaz-Moreno and coworkers [9]. The interaction between PC and Cytf has been experimentally investigated by several mutations of PC to elucidate the site of the electron transfer and the docking regions of molecules in relation to the reaction rate of the reduction reaction of PC [10].