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Vanadium—Speciation Chemistry Can Be Important When Assessing Health Effects on Living Systems
Published in Debasis Bagchi, Manashi Bagchi, Metal Toxicology Handbook, 2020
Debbie C. Crans, Kahoana Postal, Judith A. MacGregor
Numerous studies probing the fundamental biological activities of vanadium have been reported, indicating that it exerts many different activities (Costa Pessoa 2015). Vanadate (H2VO4−) is a structural and electronic analog of phosphate (H2PO4−) and can replace phosphate in some enzymes, acting as a substrate analog or as a transition state inhibitor (Crans et al. 2018, McLauchlan et al. 2015). Proteins such as phosphatases (McLauchlan et al. 2015) and serum albumin or transferrin (Pessoa and Tomaz 2010) are known to bind vanadium with high affinity. Vanadium bound to the blood proteins represents a key mechanism for distribution throughout the mammal and vanadium bound to these proteins can occur in oxidation states III, IV, and V (Pessoa and Tomaz 2010, Levina, Crans, and Lay 2017). Indeed, redox chemistry presumably in the form or Fenton chemistry has been reported with the formation of reactive oxygen species (ROS) (Willsky et al. 2011, Crans et al. 2013, Crans 2015).
Techniques of Chiroptical Spectroscopy
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Nelu Grinberg, Harry G. Brittain, Sonia Rodriguez
Schauerte et al. used their instrument to determine anisotropy factor values as small as 10−4 with subnanosecond resolution, enabling the measurement of changes in CPL on the short time scale, which is typical for protein fluorescence decay. The capabilities of their instrument was demonstrated using a model system, where they recorded the TR-CPL signal generated by (+)- and (-)-camphorequinone placed in the two compartments of a tandem cuvette. To create the time-dependent optical activity, the fluorescence decay time of one enantiomer was shortened by quenching. In subsequent experiments, the authors timed-resolved the circularly polarized emission of reduced nicotinamide adenine dinucleotide bound to horse liver alcohol dehydrogenase in the binary complex, as well as in the tight ternary complex formed in the presence of the substrate analog isobutyramide. The results showed the existence of a time-dependent CPL, while the optical activity of the ternary complex was found to be essentially time independent.
Chemical Physical and Biochemical Concepts in Isolation and Purification of Proteins
Published in Juan A. Asenjo, Separation Processes in Biotechnology, 2020
Milton T. W. Hearn, Birger Anspach
Depending on the magnitude of the different free-energy changes, a variety of solute retention versus mobile-phase elutropic strength scenarios can be calculated. Figure 4 represents four limiting cases of such retention dependencies. Case b is typified by shallow dependencies of free energy versus elution strength with low free energies at ζ (or [c] = 0) and represents a commonly observed situation with small polar peptides separated under reversed-phase or ion-exchange HPLC conditions (O’Hare and Nice, 1979; Molnàr and Horvàth, 1977; Aguilar et al., 1985). Case c, which again exhibits shallow dependencies in terms of the free energy versus eluant strength dependency but with large values of ΔG0o values, is more representative of situations found with middle molecular weight but very high hydrophobic peptides under some reversed-phase conditions; in affinity displacement ion-exchange or substrate analog displacement elution in affinity chromatography where the substrate/analog or displacing species is again typically of low molecular weight (Stout et al., 1986; Kopaciewicz et al., 1983; Gooding and Schmuck, 1984). Some examples of peptide displacement chromatography also correspond to this case. Case a represents a typical scenario for polypeptide and globular protein purification in reversed-phase and hydrophobic interaction techniques and with most polymer- and silica-based anion and cation HPLC support media (Benedek et al., 1984; Kennedy et al., 1986; Janzen et al., 1987; Lau et al., 1984; Glajch et al., 1986; Hearn and Hodder, submitted; Mant and Hodges, 1985).
Tendency of using different aromatic compounds as substrates by 2,4-DNT dioxygenase expressed by pJS39 carrying the gene dntA from Burkholderia sp. strain DNT
Published in Bioremediation Journal, 2018
Khaled M. Khleifat, Muhamad O. Al-limoun, Khalid Y. Alsharafa, Haitham Qaralleh, Amjad A. Al Tarawneh
Considering all substrates used, only p-nitrophenol showed zero oxygen uptake rate and zero growth. This indicates that it was rather unlikely that p-nitrophenol is a substrate analog for 2,4-DNT. On the other hand, Spain and Gibson (1991) showed that p-nitrophenol inhibits its own monooxygenase (p-nitrophenol monooxygenase) at low concentration. Catechol was clearly used as a sole carbon source by both wild-type E. coli (JM103) and the dnt transformant (PFJS39). Using α-naphthalene acetic acid and β-dimethylaminobenzaldehyde as substrates resulted in DNT dioxygenase oxygen uptake rates of 11.8 and 14 μM/hr/mg protein, respectively. Also when either compound was used as a carbon source, JS39 had twice the growth rate of E. coli JM103, although both had growth rates less than the controls without added compound. This is consistent with the oxygen uptake experiments in showing that DNT dioxygenase can metabolize these two substrates. Presumably, they are metabolized partially by DNT dioxygenase in strain JS39 to intermediates which are less toxic than 2, 4-DNT itself. A partially purified nitrobenzene dioxygenase from Comamonas sp. strain JS765 oxidizes a wide range of substrates, with 3-nitrotoluene as a favorably substrate, and was shown to be a growth substrate for JS765 (Lessner et al. 2002). The variation in the efficiency of substrate utilization could be affected by the condition of the medium (or assay solution) such as the availableness of oxygen, pH, and temperature as well as other components (Shawabkeh et al. 2007). For example, the bacterial growth expressed as biomass yield had a different optimum temperature and was not influenced to the same extent by variations in the carbon sources (Khleifat et al. 2006).