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The Microbial Degradation of DDT and Potential Remediation Strategies
Published in M.H. Fulekar, Bhawana Pathak, Bioremediation Technology, 2020
Conversely, while using such pollutants as TEA, energy is obtained by passing electrons to the pollutant, and hence reducing it (Figure 1.3). The halo-organic compound is used as a TEA and energy is conserved (Holliger et al., 1999; Smidt and de Vos, 2004). Energy is gained by a chemiosmotic gradient along the cell membrane, resulting in a proton motive force (PMF) which drives a membrane-bound ATPase to generate ATP (Mohn and Tiedje, 1991). Such a process can be stimulated at the field level, but requires selective stimulation of desirable organisms by the introduction of specific combinations of electron donors and acceptors (Suflita et al., 1988), as well as nutrients to meet the growth requirements of the enriched species. Hence, the choice of an electron donor and acceptor combination is crucial for the success of such processes.
Interfacial Catalysis at Oil/Water Interfaces
Published in Alexander G. Vdlkdv, Interfacial Catalysis, 2002
Reaction (2) is exothermic, and the energy can be used to transport protons across the mitochondrial membrane (Fig. 1). Mitochondrial cytochrome c oxidase is a dimer, each monomer being composed of 13 subunits. The enzyme contains cytochromes a and a3, one binuclear copper complex Cua, one mononuclear copper site Cub and one bound Mg2+ per monomer [23]. It has a molecular weight of about 180,000-200,000kDa for the most active form. Cytochrome oxidases can transport up to eight protons across the membrane per four electrons. Four of the protons bind to the reaction complex during dioxygen reduction to water and up to four other protons are transported across the membrane. The resulting chemiosmotic proton gradient is used in ATP synthesis.
Protein-Based Optical Memories
Published in Sergey Edward Lyshevski, Nano and Molecular Electronics Handbook, 2018
Jeffrey A. Stuart, Robert R. Birge, Mark P. Krebs, Xi Bangwei, William Tetley, Duane L. Marcy, Jeremy F. Koscielecki, Jason R. Hillebrecht
In its native organism, BR acts as a light-driven proton pump; proton translocation across the cell membrane is facilitated by the protein, and the resulting electrochemical gradient (ΔpH ≈ 1) is used by the cell to do work. The proton gradient fuels ATP synthesis through a standard F0F1 ATPase, and served as one of the first examples of chemiosmosis [37–39]. As mentioned earlier, the retinal chromophore mediates light to chemical energy transduction by the protein. A light-induced isomerization of the chromophore initiates a series of events in the protein that ultimately results in the translocation of a proton across the cell membrane. This process is described by the protein’s photocycle, a series of spectrally distinct intermediates (Figure 16.2) that characterizes the step-wise process of passing a proton across the membrane. The intermediates are produced sequentially, and are denoted as the K, L, M, N, and O states (see Figure 16.1). A branch off of the O-state accesses the P and Q states, which will be discussed later. Historically, the observable intermediates were defined by thermal trapping [40]. Each intermediate is characterized by a combination of factors, including the wavelength of maximum absorption, lifetime, chromophore configuration (isomerization state and overall conformation), the electronic environment of the binding site, the protonation state of the retinal Schiff base, and both the protonation state and orientation of key amino acids in the proton channel (reflecting the progress of a proton across the membrane). Light-induced chromophore isomerization from all-trans to 13-cis, often referred to as the primary event, results in a shift in electron density toward the protonated Schiff base during the formation of the K-state, the only photochemically generated state in the native photocycle. The bR→K transition proceeds with an impressive quantum efficiency of ~ 65%. The redistribution of charge changes the electrostatic nature of the binding site and provides the motive force that drives the formation of subsequent thermal intermediates (i.e., L, M, N, and O), and, ultimately, proton translocation. A branch off of the O-state has two additional intermediates, P and Q. The blue-shifted M and Q states are of the most interest to optical device applications. On average, the protein can go through this cycle > 106 times (a benchmark known as the cyclicity). The proton-pump mechanism is well described in the literature [41–52].
Biochemical characterization of a partially purified protease from Aspergillus terreus 7461 and its application as an environmentally friendly dehairing agent for leather industry
Published in Preparative Biochemistry & Biotechnology, 2021
Emmly Ernesto de Lima, Daniel Guerra Franco, Rodrigo Mattos Silva Galeano, Nelciele Cavalieri de Alencar Guimarães, Douglas Chodi Masui, Giovana Cristina Giannesi, Fabiana Fonseca Zanoelo
The activity and stability of the partially purified protease from A. terreus were evaluated at different values of pH and temperatures (Fig. 3). Because the pH value of the medium affects the proton motive force in chemiosmosis, under the optimum pH range it is possible to achieve high metabolic efficiency. Hence, pH is a very critical factor that should be optimized.[5] The protease of the present study was active between pH 6.0 and 10.0, showing maximum activity at pH 6.5 (Fig. 3A), results that were similar to other studies. Chakrabarti et al.[39] for example, showed that A. terreus IJIRA 6.2 serine protease showed broad activity (pH 4.0 − 12.0) with a maximum peak at pH 8.5. Niyonzima and More[32] working with a protease from A. terreus demonstrated that the enzyme was inactivated at low pH and was active at alkaline pH (8.0−12.0) with maximum activity at pH 11.0. And the Hirsutella rhossiliensis OWVT-1 serine protease showed ideal activity at pH 7.0.[40] All these reports showed proteases with optimal pHs ranging from neutral to alkaline, corroborating our results.