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Microbiomes and Metallic Nanoparticles in Remediation of Contaminated Environments
Published in Vivek Kumar, Rhizomicrobiome Dynamics in Bioremediation, 2021
Ana Maria Queijeiro López, Amanda Lys dos Santos Silva, Elane Cristina Lourenço dos Santos, Jean Phellipe Marques do Nascimento
Numerous reports emphasize the identification of two distinct ATP-producing mechanisms, i.e. oxidative phosphorylation and substrate-level phosphorylation (Hunt et al. 2010, Kane et al. 2016, Pinchuk et al. 2011). Oxidative phosphorylation is typically associated with respiration, in which the reduction of terminal electron acceptors is coupled to proton motive force (PMF) generation, which subsequently contributes to ATP-synthesis via ATP synthase. Substrate level phosphorylation is associated with the production of ATP through direct transfer of a phosphoryl group to ADP, using enzymes such as phosphotransacetylase and acetate kinase. In the context of gold-NPs, bacteria able to reduce the Au3+ ions into Au° in the nanoscale are important, such as Shewanella oneidensis MR-1 and other Shewanella species that utilize a broad range of electron acceptors, making this genus a model for research of anaerobic respiration and metabolic energy conservation. The substrate-level phosphorylation of S. oneidensis strain MR-1, for instance, is the primary source of ATP during anaerobic growth, while ATPase has either minor contributions to ATP production or acts as an ATP-driven proton pump that generates PMF (Hunt et al. 2010). This was surprising, given that Shewanella bacteria are obligated to utilize terminal electron acceptors when growing under anaerobic conditions.
An investigation of natural nano-particles for cleaning
Published in Matthew Laudon, Bart Romanowicz, 2007 Cleantech Conference and Trade Show Cleantech 2007, 2019
Enzymes are proteins that catalyze (i.e. accelerate) chemical reactions. In these reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products. Almost all processes in the cell need enzymes in order to occur at significant rates. Since enzymes are extremely selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell. Like all catalysts, enzymes work by lowering the activation energy (ΔG‡) for a reaction, thus dramatically accelerating the rate of the reaction. Most enzyme reaction rates are millions of times faster than those of comparable uncatalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions. However, enzymes do differ from most other catalysts by being much more specific.
Principles of Chemistry
Published in Arthur T. Johnson, Biology for Engineers, 2019
A substrate is any substance on which an enzyme can act to form a product. Rates of simple enzyme–substrate reactions are often described by the Michaelis–Menten construction. It has been found that the rate of product formation depends directly on the substrate concentration, but that the dependence is small for low substrate concentrations and for high substrate concentrations, and the dependence is highest somewhere between. The curve of rate of product formation plotted against substrate concentration forms an “S” shape (Figure 3.5.1). The steeper the “S,” the higher is the affinity of the enzyme for the substrate. A typical enzyme-substrate system has a rate of product formation equal to half the maximum (saturation) rate at about 5 mM at room temperature. Changing the concentration of an enzyme will affect the position of the curve.
Thermal damages in spray drying: Particle size-dependent protein denaturation using phycocyanin as model substrate
Published in Drying Technology, 2023
Nora Alina Ruprecht, Reinhard Kohlus
In a food matrix, proteins serve functional properties such as foaming, gelling, and emulsifying which influence the product texture, appearance, and stability. The functional properties are determined by the protein conformation. For instance, the surface activity, and thus, their ability to stabilize interphases, is defined by the exposed amino acids of a protein.[27] Some proteins also serve biological functions, which are determined by their structure. Enzymes catalyze reactions, if the shape of their active site is compatible with the shape of the substrate.[28] Protein denaturation causes an unfolding of the three-dimensional structure, which changes their functionality and in consequence alters the product.[29]
Intracellular-to-extracellular localization switch of acidic lipase in Enterobacter cloacae: evaluation of production kinetics and enantioselective esterification potential for pharmaceutical applications
Published in Preparative Biochemistry & Biotechnology, 2023
Atim Asitok, Maurice Ekpenyong, Nkpa Ogarekpe, Richard Antigha, Iquo Takon, Anitha Rao, Juliet Iheanacho, Sylvester Antai
Substrate specificity is a function of enzyme conformation or structure, especially at the active site, substrate structure and prevailing factors that influence enzyme-substrate binding.[43]p-NP-laurate (C12) was selected as best substrate for E. cloacae lipase with a relative activity of 162.48% (Figure 2B). This was followed by p-NP-myristate (C14) with 133.47%. Dunnet’s test of multiple comparison showed that mean differences between all p-nitrophenol-ester were significantly different from the control except that between control and p-NP-stearate. Similar results have earlier been reported for acidic lipase from Candida viswanathii.[13] However, selection of an optimum fatty acyl substrate may be strain-specific, in addition to the inherent structural differences among lipases, no matter how small.
Cloning, expression, and characterization of an arabitol dehydrogenase and coupled with NADH oxidase for effective production of L-xylulose
Published in Preparative Biochemistry & Biotechnology, 2022
Chen-Yuan Zhu, Yi-Hao Zhu, Hua-Ping Zhou, Yuan-Yuan Xu, Jian Gao, Ye-Wang Zhang
In order to study the application of the ArDH-SmNox coupled SmNox system in higher xylitol concentrations, the influence of various xylitol concentrations on the enzymatic conversion was investigated. The reaction rate is affected by the substrate concentration, and high substrate concentration may inhibit the enzymatic reaction.[39,40] Herein, the catalytic activity of ArDH was evaluated using various concentrations (from 10 to 80 mM) of xylitol as substrate (Figure 5). The results revealed that 92.7% of yield was obtained after 8 h with 10 mM xylitol. In addition, when using the whole-cell to produce L-xylulose, it is difficult to obtain a high yield in high substrate concentrations due to the diffusional limitation of the substrate into the cell. Then, compared with the microbial strategy, a higher L-xylulose yield with a high concentration substrate was achieved because there is no diffusion restriction of the cell wall.[17,31] However, the conversion decreased sharply to 18.4% when the xylitol concentration was increased to 80 mM. This could be the product inhibition of the ArDH. To improve the yield at high concentration substrate or in industrial production, in situ product removal could be a good choice which will facilitate the equilibrium shift to the product.[41]