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Structures
Published in Thomas M. Nordlund, Peter M. Hoffmann, Quantitative Understanding of Biosystems, 2019
Thomas M. Nordlund, Peter M. Hoffmann
Two of the common reducing agents in biosystems are NADH and NADPH, shown in Figure 5.7. These molecules are dinucleotides (note again the presence of the adenine base) because they are made of two nucleotides joined through their phosphate groups. One nucleotide has an adenine base, the other nicotinamide, which is not a normal base used in DNA. NAD+ accepts two electrons and a proton from other molecules and becomes reduced NADH, which can then be used as a reducing agent to donate electrons. Such electron transfer reactions are the main function of NAD+/NADH. However, it is also used as a substrate of enzymes that add or remove chemical groups from proteins, immediately after the proteins are synthesized. The NAD+/NADH ratio in living cells is an important component of what is called the “redox state” of a cell, a quantity that reflects the activity and the health of cells. In plant chloroplasts, NADP+ is reduced by the enzyme ferredoxin-NADP+ reductase during photosynthesis. The NADPH produced is then used as reducing power for the biosynthetic reactions in the Calvin cycle of photosynthesis. In animals, NADPH provides the reducing equivalents for biosynthetic reactions (lipid and cholesterol synthesis and fatty acid chain elongation) and for oxidation-reduction involved in protection against the toxicity of reactive oxygen species. Both NADH and NADPH are termed coenzymes because they bind to enzymes and help catalyze reactions. The molecular masses of NADH and NADPH are 663 and 745 Da (without counterions), respectively, so they are borderline “small.” Note also that the net charge of NAD+ (NADH) is −1 (−2); that of NADP+ (NADPH) is −3 (−4).
Algae-Mediated Bioelectrochemical System: The Future of Algae in the Electrochemical Operations
Published in Kuppam Chandrasekhar, Satya Eswari Jujjavarapu, Bio-Electrochemical Systems, 2022
Rehab H. Mahmoud, Hany Abd El-Raheem, Rabeay Y.A. Hassan
In microalgae, light energy conversion occurs through two reaction centers: photosystems 1 (PSI) and photosystems 2 (PSII), which are protein multiplexes buried in the membrane of the thylakoid (Yadavalli et al., 2020, 2021). PS1, as well as PS2, are connected and interact via a chain of electron carriers that includes enzymes and co-factors such as ferredoxin (Fd), the cytochrome (Cyt) b6f complex, plastocyanin (PC), and plastoquinone (PQ). The electron carriers are responsible for transporting electrons expelled during photosynthetic water splitting to the ultimate electron acceptor, nicotinamide adenine dinucleotide phosphate (NADP+). Essentially, electrons are transferred from lower-potential electron carriers to higher-potential electron carriers. In a nutshell, chlorophyll antenna light absorption activates the PSII, which then sends its energy to P680 (the PSII primary donor). Water splitting and electron transport pathways throughout the chain (plastoquinone (PQ)/plastoquinol (PQH2) pool/cytochrome b6f (b6f)/plastocyanin (PC)/Photosystem I (PSI)/Ferredoxin (Fd)/Ferredoxin-NADP reductase (FNR)) result in NADP reduction (Figure 4.1). The Calvin cycle finally culminates in the decrease of CO2 via sequential ATP synthesis by ATP synthase. Taking benefit from the photosynthesis process essentially occurs by using an exterior polarized electrode with high electrochemical activity for gathering a fraction of the electron flow along the photosynthetic chain (Sayegh et al., 2019). Photosystems (PSII and PSI) have been separated as photochemical converters to enhance electron transport between photosynthetic microbes and electrode surfaces in several studies (Kato et al., 2014; Sayegh et al., 2019; Tel‐Vered & Willner, 2014). Nonetheless, it brings up the question of these systems' flexibility outside of their biological environment. As a result, isolated thylakoid membranes or chloroplasts are also taken into account (Calkins et al., 2013; Hasan et al., 2014). However, the lack of cell proliferation in these two techniques is a significant issue that necessitates further research into entire photosynthetic organisms (Grattieri et al., 2017; Hasan et al., 2017; Sekar et al., 2014). Hence, the electron transport routes to the electrode get more complicated as the target becomes more complex. In fact, energy harvesting directly from a photosynthetic microorganism organism is uncommon (Kim et al., 2016; Kim et al., 2018; Ryu et al., 2010). So, to boost photocurrent production, electron shuttles such as soluble mediators (quinones Fe(CN)-36), redox polymers, and nano-objects are used as supplementary agents (Sekar & Ramasamy, 2015).
Hazards assessment of the intake of trace metals by common mallow (Malva parviflora K.) growing in polluted soils
Published in International Journal of Phytoremediation, 2019
Tarek M. Galal, Zeinab A. Shedeed, Loutfy M. Hassan
In addition, Appenroth (2010) reported the adverse effects of trace/heavy metals on the light and dark reactions of photosynthesis as well as on the reduction of chlorophyl content, stomatal conductance, and transpiration rates. Moreover, several mechanisms have been proposed for metals-induced decrease in pigment contents, which include distorted chloroplast ultra-structure, decrease in the activities of delta- aminolevulinic acid dehydratase and ferredoxin NADP + reductase, inhibition of plastoquinone and carotenoid synthesis, hindrance in electron transport chain, and Calvin cycle inhibition (Pourrut et al.2013). These mechanisms include: (a) some elements (as Pb) reduce the uptake of chlorophyl-essential elements such as Mg and Fe; (b) decreasing rate of photosynthetic pigment accumulation (with Pb treatment) may be the consequence of peroxidation of chloroplast membranes due to increased level of ROS generation (Malar et al.2014); and (c) the concomitant pheophytin accumulation and oxidative stress have been observed in plants exposed to toxic concentrations of elements (Mobin and Khan 2007; Gomes et al.2016). This is because, under stress conditions, part of chlorophylls might be converted to pheophytins (Pheophytins are compounds formed during the chlorophyl degradation [Sanmartin et al.2011]).
Comparative proteomic analysis revealed the metabolic mechanism of excessive exopolysaccharide synthesis by Bacillus mucilaginosus under CaCO3 addition
Published in Preparative Biochemistry & Biotechnology, 2019
Hongyu Xu, Zhiwen Zhang, Hui Li, Yujie Yan, Jinsong Shi, Zhenghong Xu
ATP synthases are membrane-bound enzymes that use the energy derived from an electrochemical proton gradient for ATP formation.[35] Ferredoxin–NADP reductase (Fpr) controls the NADP+/NADPH pool in heterotrophic organisms, such as bacteria. Fpr functions as an electron carrier between the electron donor and ferredoxin/flavodoxin to ferredoxin/flavodoxin reductase and pushes the synthesis of ATP simultaneously.[36] The biosynthesis of bacterial extracellular polysaccharides is a capacity-intensive process, in which a precursor of a synthetic nucleoside is synthesized, a glycosyl phosphorylase phosphorylates a glycosyl group, and a glycosyltransferase converts a monosaccharide into a unit of human polysaccharide synthesis. Polymerizing long chains of polysaccharides consumes energy.[37,38] The cells under CaCO3 addition generated additional ATP necessary for metabolism and the polymerization of precursor to form BMPS and excretion of BMPS to the culture broth, than that in the absence of the supplement.
Lead-induced modification of growth and yield of Linum usitatissimum L. and its soil remediation potential
Published in International Journal of Phytoremediation, 2023
Adnan Khan, Athar Ali Khan, Mohd Irfan, Mohd Sayeed Akhtar, Syed Aiman Hasan
The only way for solar energy to enter the ecosphere in a useful form is through chloroplasts. As a result, any change in chloroplast structure or chlorophyll concentration will affect gross and net primary production at the producer level, as well as the amount of energy available at higher trophic levels. A well-known plant response to heavy metal stress, such as Pb, is a decrease in chlorophyll concentration (Figure 2c) (Tiwari and Lata 2018). According to Pourrut et al. (2011), distorted chloroplast structure, decreased activity of ferredoxin NADP+ reductase and δ-aminolevulinic acid dehydratase, inhibited plastoquinone and carotenoid synthesis, obstructed electron transport system, reduced CO2 level via stomata closure, impaired uptake of essential elements and substitution of divalent cations by Pb, reduced Calvin cycle enzyme activity. Figure 2a,b shows a greater decline in Chl. b concentration, confirming previous observations (Seregin et al. 2004; Ashraf et al. 2015; Malar et al. 2016). Rise in cellular proline level (Figure 2d) is a well-known biochemical response of plants to abiotic stresses (Rana et al. 2017) and it is ascribed to any one or more of the four processes (a) de novo synthesis (b) decreased degradation (c) lower utilization and, (d) hydrolysis of proteins (Kaur and Asthir 2015). As reported earlier in plants like rice, wheat, and spinach by various scientists (Alia et al. 2015; Ashraf et al. 2017; Malik et al. 2021) Pb stress caused a significant increase in proline level in the leaves of plants, a strategy of plants to cope up with Pb stress (Malar et al. 2016; Ashraf et al. 2017; Malik et al. 2021).