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Carbon Dioxide Sequestration by Microalgae
Published in Gokare A. Ravishankar, Ranga Rao Ambati, Handbook of Algal Technologies and Phytochemicals, 2019
G.V. Swarnalatha, Ajam Shekh, P.V. Sijil, C.K. Madhubalaji, Vikas Singh Chauhan, Ravi Sarada
RuBisCO is one of the major enzymes responsible for fixation of atmospheric CO2 to organic carbon in microalgae. This enzyme shows less affinity towards CO2, and O2 is a competitive substrate for CO2 which may lead to photorespiration. Therefore, when O2 is increased and CO2 is decreased in the atmosphere, it affects the carboxylase activity of RuBisCO due to decreased ratio of CO2:O2. The source of CO2 required for the photosynthesis for the aquatic organisms is from surrounding water in which the CO2 diffuses 10,000 times slower than it does in the air. In order to enhance the CO2 concentration in the vicinity of RuBisCO for improved photosynthesis, these aquatic organisms have an inorganic CCM inside the cell (Hwangbo et al. 2018) which enhances the uptake of CO2 (Swarnalatha et al. 2015). The CO2 tolerance and biofixation rates of various microalgal strains are given in Table 6.2.
Impact of Sulphur Dioxide Deposition on Medicinal Plants' Growth and Production of Active Constituents
Published in Azamal Husen, Environmental Pollution and Medicinal Plants, 2022
Shakeelur Rahman, Azamal Husen
Plant metabolism is affected by SO2 by either accepting or donating electrons that impact the cellular electron transport system in plants (Osmond and Avadhani 1970). Lipid peroxidation in plants is guided by exposure to a higher concentration of SO2 (Li and Yi, 2012). The chlorophyll content of plants works as a biomarker for air pollution levels (Darrall and Jager 1984). Chlorophyll is converted into phaeophytin by SO2 with the release of Mg2+ by reducing the pH and altering the spectral characters (Rao and Leblanc 1965). Some of the enzymes become inactivated because of breaking of the disulfide bridges (Cecil and Wake 1962) or, by inducing some conformational changes, some hydrolytic enzymes may even be activated (Malhotra and Hocking 1976). SO2 also affects the photosynthetic CO2 fixation; as a result, RuBisCO is inhibited by the higher concentration of SO2 by competing with CO2 or bicarbonate for the binding sites in RuBP carboxylase (Zeigler 1972). Different findings show that SO2 also had an impact on respiration (Gheorghe and Ion 2011). Glutathione reductase (GR) enzymes engaged in the antioxidant defence system are shown to be expressed at elevated levels when exposed to SO2. Lorenzini et al. (1995) reported the gas-exchange reaction of two-year-old oak seedlings (Quercus pubescens) exposed to SO2 showed a significant linear decrease in stomatal conductance, photosynthetic activity, water use efficiency, and transpiration rate. However, total sulphur content and foliar starch increased linearly with increasing SO2 concentration. It was observed that the genetic differences between the ecotypes of Geranium carolinianum affected physiological expression of different biochemical threshold levels of response to SO2 (Taylor et al. 1986).
An overview on the recently discovered iota-carbonic anhydrases
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2021
Alessio Nocentini, Claudiu T. Supuran, Clemente Capasso
In plants, CO2 is stored as bicarbonate ions. In both terrestrial and aquatic plants, CA converts HCO3- ions to CO2, which is concentrated in the proximity of the enzyme RuBisCO (Ribulose Bisphosphate Carboxylase/Oxygenase) present in the stroma of the chloroplasts13–15. As a result, the performance of RuBisCO carboxylation reaction is increased, whereas its oxygenation is suppressed. Eukaryotic unicellular photosynthetic organisms have evolved diverse Carbon Concentrating Mechanisms (CCMs) to increase CO2 concentration in the proximity of RuBisCO up to 1000-fold from the low CO2 levels present in the environment. In algae, the main component of the CCM is the pyrenoid16,17. In cyanobacteria, the equivalent of the pyrenoid is the carboxysome. Carboxysomes are composed of RuBisCO, CAs, active bicarbonate transporters, and structural envelope proteins18. The structure of the carboxysome envelope prevents the escape of CO2 from these organelles.
Hydrogen deuterium exchange mass spectrometry applied to chaperones and chaperone-assisted protein folding
Published in Expert Review of Proteomics, 2019
Florian Georgescauld, Thomas E. Wales, John R. Engen
HDX MS methodology has also been applied to the AAA+ molecular machinery involved in protein remodeling. One study concerned the mechanism of the AAA+ protein Rubisco activase in the repair of the photosynthetic enzyme Rubisco, a complex of eight large and eight small subunits [58]. Another study used HDX MS to monitor complex formation in Cdc48 [59]. The conformational dynamics of Hsp104, also an AAA+ molecular machine that rescues proteins trapped in amorphous aggregates and stable amyloids, have been studied by HDX MS [60]. Finally, HDX MS was used by the groups of Martin and Hurley to show that the ATPaseVps4 disassembles an ESCRT-III filament by global unfolding and processive translocation [61], while the peroxisomal ATPase Pex1/Pex6 unfolds substrates by processive threading [62]. For all these studies, HDX MS was used to better understand the dynamic aspects of these AAA+ machines during their functional cycle and their interaction(s) with substrates or various partners. The structural information obtained by HDX MS could hardly have been obtained by other structural methods and shows the growing role of this technique in understanding how large protein machines perform their biological functions.
Still challenging: the ecological function of the cyanobacterial toxin microcystin – What we know so far
Published in Toxin Reviews, 2018
Azam Omidi, Maranda Esterhuizen-Londt, Stephan Pflugmacher
Proteomics studies revealed the potential role of MCs in protection against oxidative stress as MC bound covalently to the cysteine residues of certain proteins via its N-methyl-dehydroalanine moiety (Dziallas & Grossart, 2011; Kaplan et al., 2012; Zilliges et al., 2011). These proteins include phycobiliproteins, CpcB and ApcA, RuBisCo, glutathione reductase, and various hypothetical proteins that were expressed differentially in the wild-type and mutant strain (Zilliges et al., 2011). Under oxidative stress due to the iron depletion, MCs showed a greater tendency to the binding sites in thioredoxin-regulated proteins (Alexova et al., 2016). On one hand, in M. aeruginosa PCC 7806 wild--type grown under high light and iron deficiency or exposed to 10 μM hydrogen peroxide, MC-protein formation was stimulated. On the other hand, in cultures treated with a protease such as subtilisin under high light (51 800 lm m−2), the large subunit of RuBisCo was more stable in the wild type. It was assumed that MC attachment to proteins avoid the dimerization of cysteines and consequently caused a delay in conformational changes of proteins and enzymes inactivation (Zilliges et al., 2011). Thus, the increased protein stability led to more adaptation to the various stresses (Kaplan et al., 2012; Zilliges et al., 2011). Moreover, under high light, the decreased oxygenase function of RuBisCo protected the cells against photorespiration (Gerbersdorf, 2006). On the contrary, current findings indicated MCs as additional radical scavengers which might protect the cells against oxidative stress damage (Martin-Luna et al., 2006a, Zilliges et al., 2011). The ability of MCs to bind to metals such as zinc and cadmium also point to the possible role of the toxin in metal detoxification in metal-induced oxidative stresses (Dziallas & Grossart, 2011).