Degradation of PFOS by a MnO2/H2O2 process

Levels of oxidized low-density lipoproteins (oxLDLs) are usually low in vivo but can increase whenever the balance between formation and scavenging of free radicals is impaired. Under normal conditions, uptake and degradation represent the physiological cellular response to oxLDL exposure. The uptake of oxLDLs is mediated by cell surface scavenger receptors that may also act as signaling molecules. Under conditions of atherosclerosis, monocytes/macrophages and vascular smooth muscle cells highly exposed to oxLDLs tend to convert to foam cells due to the intracellular accumulation of lipids. Moreover, the atherogenic process is accelerated by the increased expression of the scavenger receptors CD36, SR-BI, LOX-1, and SRA in response to high levels of oxLDL and oxidized lipids. In some respects, the effects of oxLDLs, involving cell proliferation, inflammation, apoptosis, adhesion, migration, senescence, and gene expression, can be seen as an adaptive response to the rise of free radicals in the vascular system. Unlike highly reactive radicals, circulating oxLDLs may signal to cells at more distant sites and possibly trigger a systemic antioxidant defense, thus elevating the role of oxLDLs to that of signaling molecules with physiological relevance.

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Functional role of residues involved in substrate binding of human 4-hydroxyphenylpyruvate dioxygenase

Biochemical Journal ◽

10.1042/bcj20210005 ◽

2021 ◽

Author(s):

Chih-Wei Huang ◽

Chi-Ching Hwang ◽

Yung-Lung Chang ◽

Jen-Tzu Liu ◽

Sheng-Peng Wu ◽

...

Keyword(s):

Binding Affinity ◽

Functional Role ◽

Substrate Binding ◽

Critical Role ◽

Intermediate Formation ◽

Hydroxyl Group ◽

Double Mutation ◽

Closed Conformation ◽

Bond Network

4-Hydroxylphenylpyruvate dioxygenase (HPPD) catalyzes the conversion of 4-hydroxylphenylpyruvate (HPP) to homogentisate, the important step for tyrosine catabolism. Comparison of the structure of human HPPD with the substrate-bound structure of A. thaliana HPPD revealed notably different orientations of the C-terminal helix. This helix performed as a closed conformation in human enzyme. Simulation revealed a different substrate-binding mode in which the carboxyl group of HPP interacted by a H-bond network formed by Gln334, Glu349 (the metal-binding ligand), and Asn363 (in the C-terminal helix). The 4-hydroxyl group of HPP interacted with Gln251 and Gln265. The relative activity and substrate-binding affinity were preserved for the Q334A mutant, implying the alternative role of Asn363 for HPP binding and catalysis. The reduction in kcat/Km of the Asn363 mutants confirmed the critical role in catalysis. Compared to the N363A mutant, the dramatic reduction in the Kd and thermal stability of the N363D mutant implies the side-chain effect in the hinge region rotation of the C-terminal helix. The activity and binding affinity were not recovered by double mutation; however, the 4-hydroxyphenylacetate intermediate formation by the uncoupled reaction of Q334N/N363Q and Q334A/N363D mutants indicated the importance of the H-bond network in the electrophilic reaction. These results highlight the functional role of the H-bond network in a closed conformation of the C-terminal helix to stabilize the bound substrate. The extremely low activity and reduction in Q251E’s Kd suggest that interaction coupled with the H-bond network is crucial to locate the substrate for nucleophilic reaction.

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Role of Interstitial Voids in Oxides on Formation and Stabilization of Reactive Radicals: Interstitial HO2Radicals in F2-Laser-Irradiated Amorphous SiO2

Journal of the American Chemical Society ◽

10.1021/ja0571390 ◽

2006 ◽

Vol 128 (16) ◽

pp. 5371-5374 ◽

Cited By ~ 9

Author(s):

Koichi Kajihara ◽

Masahiro Hirano ◽

Linards Skuja ◽

Hideo Hosono

Keyword(s):

Amorphous Sio2 ◽

Reactive Radicals

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Reactive Radicals on Reactive Surfaces: Heterogeneous Processes in Catalysis and Environmental Pollution Control

Progress in Reaction Kinetics and Mechanism ◽

10.3184/007967405779134038 ◽

2005 ◽

Vol 30 (3) ◽

pp. 145-213 ◽

Cited By ~ 29

Author(s):

Christopher J. Rhodes

Keyword(s):

Pollution Control ◽

Surface Defects ◽

Practical Investigations ◽

Heterogeneous Reactions ◽

Molecular Surface ◽

Spin Resonance ◽

Heterogeneous Processes ◽

Tunnelling Microscopy ◽

Reactive Radicals

Many reactions that occur on solid surfaces are mediated by free radicals. A review is presented of both mechanistic and practical investigations in relation to catalysis and environmental applications. The review begins with actual imaging of surface adsorbed reactive radicals using scanning tunnelling microscopy (STM), and then discusses a range of examples, mainly as underpinned by electron spin resonance (ESR) measurements. Included are surface defects and their reactions, studies of the redox behaviour of zeolites, and the use of radicals adsorbed in zeolites as molecular surface probes of diffusion and reactivity within these important materials. Photocatalysis, mainly using TiO2-based materials, is reviewed both from the fundamental perspective and in terms of some practical examples relating to pollution control. Other reactive oxide surfaces are considered, including silica, and the nature of paramagnetic centres that may be induced thereon by a variety of activation procedures. Evidence is presented for the formation of radical species during heterogeneous reactions on metal surfaces. Finally, the role of free radical generation in creating and modifying polymer and nanomolecular systems is discussed, and the health implications of the ability of some solids such as quartz to generate reactive oxygen radicals in contact with biological media.

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Role of surfactants in optimizing fluorene assimilation and intermediate formation by Rhodococcus rhodochrous VKM B-2469

Bioresource Technology ◽

10.1016/j.biortech.2008.06.059 ◽

2009 ◽

Vol 100 (2) ◽

pp. 839-844 ◽

Cited By ~ 20

Author(s):

Marina P. Kolomytseva ◽

Dimetrio Randazzo ◽

Boris P. Baskunov ◽

Andrea Scozzafava ◽

Fabrizio Briganti ◽

...

Keyword(s):

Intermediate Formation ◽

Rhodococcus Rhodochrous

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Quantitative studies of the role of alkenes during the combustion of alkanes

Australian Journal of Chemistry ◽

10.1071/ch9702309 ◽

1970 ◽

Vol 23 (11) ◽

pp. 2309 ◽

Cited By ~ 3

Author(s):

T Berry ◽

CF Cullis

Keyword(s):

Molecular Weight ◽

Major Part ◽

Reaction Rate ◽

Intermediate Formation ◽

Substantial Proportion ◽

Lower Molecular Weight ◽

Direct Oxidation ◽

Quantitative Studies

Studies of the combustion of n-butane in the presence of small amounts of [1-14C]but-1-ene and [2-14C]but-2-ene have enabled the role and importance of the two alkenes in the oxidation of the alkane to be determined quantitatively. Thus at 315�, at a stage when the reaction rate has started to decline, over one-third of the n-butane which has reacted has been oxidized to butenes and nearly two-thirds of these two alkenes has reacted further to give other products. All the larger-ring oxa-heterocyclic products and the major part of the oxirans arise by a mechanism not involving the intermediate formation of C4 alkenes but a substantial proportion of the 2-ethyloxiran and 2,3-dimethyloxiran are formed by the direct oxidation of but-1-ene and but-2-ene respectively. About one-quarter of the C4 ketones and an appreciable part of the lower molecular weight aldehydes also appear to be formed by an alkenic route. The general conclusion which emerges is that at the temperature concerned butenes play an important but not overwhelming role as intermediates in the combustion of n-butane.

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Reactions between iron porphyrins and tetrahydropterins

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424604000258 ◽

2004 ◽

Vol 08 (03) ◽

pp. 265-278 ◽

Cited By ~ 4

Author(s):

Daniel Mansuy ◽

Delphine Mathieu ◽

Pierrette Battioni ◽

Jean-Luc Boucher

Keyword(s):

Radical Reaction ◽

Intermediate Formation ◽

Redox Potentials ◽

Iron Porphyrins ◽

General Reaction ◽

Cytochromes C ◽

The One ◽

Catalytic Cycles ◽

Electron Transfers

Data from the last few years have revealed a novel biological role of the tetrahydrobiopterin ( H 4 B ) cofactor, in one-electron transfers to the heme of the active site of NO-synthases (NOSs) with intermediate formation of a H 4 B -derived radical. These electron transfers play a key role in the catalytic cycles of the two steps catalyzed by NOS, the N ω-hydroxylation of L-arginine, and the three-electron oxidation of N ω-hydroxyarginine to L-citrulline and NO. Recent experiments performed between various tetrahydropterins and iron porphyrins have shown that the one-electron transfer from tetrahydropterins, such as the natural cofactors H 4 B and tetrahydrofolate or the synthetic 6,7-dimethyltetrahydropterin (diMeH4P), to Fe(III) porphyrins of sufficiently high redox potentials (> about -100 mV versus NHE for the Fe(III)/Fe(II) couple) is a very general reaction that occurs with formation of a tetrahydropterin-derived radical. Reaction of diMeH4P with a stable porphyrin Fe(II)-O 2 complex leads to a diMeH4P-derived radical and a transient Fe(III)-OOH complex, mimicking the reaction between H 4 B and heme Fe(II)-O 2 in the NOS catalytic cycle. Tetrahydropterins such as diMeH4P also reduce hemeproteins Fe(III) of sufficiently high redox potentials, such as cytochromes c and b5 or metmyoglobin, to the corresponding hemeproteins Fe(II) .

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