DSpace Angular :: Browsing by Author "Davies, Michael J."

Browsing by Author "Davies, Michael J."

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3-Hydroxykynurenine bound to eye lens proteins induces oxidative modifications in crystalline proteins through a type I photosensitizing mechanism
(2019) Avila, Felipe; Ravello, Natalia; Zanocco, Antonio L.; Gamon, Luke F.; Davies, Michael J.; Silva, Eduardo
Photosensitized reactions mediated by endogenous chromophores have been associated with the etiology of age-related cataract disease. Endogenous chromophores such as 3-hydroxykynurenine (3OHKN) can be found in both free form, and bound to crystallin proteins. However, their efficiency in generating photo-induced oxidative modifications on eye lens proteins is not completely understood. In this work, the efficiency and photodynamic activity of 3OHKN bound to both lysine (3OHKN-Lys) and bovine lens proteins (3OHKN-BLP) was assessed and compared with the photosensitizing activity of the major chromophore arising from glucose degradation (GDC). The photosensitizing activity of 3OHKN-Lys, 3OHKN-BLP and GDC was characterized by measurement of singlet oxygen quantum yields, O-2 consumption, SDS-PAGE and amino acid analysis of the photo-oxidized proteins.
Aggregation of alpha- and beta- caseins induced by peroxyl radicals involves secondary reactions of carbonyl compounds as well as di-tyrosine and di-tryptophan formation
(2018) Fuentes Lemus, Eduardo Felipe; Silva, Eduardo; Barrias, Pablo; Aspee, Alexis; Escobar Álvarez, Elizabeth; Lorentzen, Lasse G.; Carroll, Luke; Leinisch, Fabian; Davies, Michael J.; López Alarcón, Camilo Ignacio
Azocompounds as generators of defined radical species: Contributions and challenges for free radical research
(2020) López Alarcón, Camilo Ignacio; Fuentes Lemus, Eduardo Felipe; Figueroa Alegría, Juan David; Dorta, Eva; Schöneich, Christian; Davies, Michael J.
Peroxyl radicals participate in multiple processes involved in critical changes to cells, tissues, pharmacueticals and foods. Some of these reactions explain their association with degenerative pathologies, including cardiovascular and neurological diseases, as well as cancer development. Azocompounds, and particularly AAPH (2,2 ' Azobis(2-methylpropionamidine) dihydrochloride), a cationic water-soluble derivative, have been employed extensively as sources of model peroxyl radicals. A considerable number of studies have reported mechanistic data on the oxidation of biologically-relevant targets, the scavenging activity of foods and natural products, and the reactions with, and responses of, cultured cells. However, despite the (supposed) experimental simplicity of using azocompounds, the chemistry of peroxyl radical production and subsequent reactions is complicated, and not always considered in sufficient depth when analyzing experimental data. The present work discusses the chemical aspects of azocompounds as generators of peroxyl (and other) radicals, together with their contribution to our understanding of biochemistry, pharmaceutical and food chemistry research. The evidence supporting a role for the formation of alkoxyl (RO center dot) and other radicals during thermal and photochemical decomposition of azocompounds is assessed, together with the potential influence of such species on the reactions under study.
Binding of rose bengal to lysozyme modulates photooxidation and cross-linking reactions involving tyrosine and tryptophan
(2019) Fuentes Lemus, Eduardo Felipe; Mariotti, Michele; Hägglund, Per; Leinisch, Fabian; Fierro Huerta, Angélica; Silva, Eduardo; López Alarcón, Camilo Ignacio; Davies, Michael J.
Chemical Modification of Lysozyme, Glucose 6-Phosphate Dehydrogenase, and Bovine Eye Lens Proteins Induced by Peroxyl Radicals : Role of Oxidizable Amino Acid Residues
(2013) Arenas, Andrea; López Alarcón, Camilo Ignacio; Kogan Bocian, Marcelo; Lissi Gervaso, Eduardo A.; Davies, Michael J.; Silva Stevens, Eduardo Andrés
Complexation of AAPH (2,2′-azobis(2-methylpropionamidine) dihydrochloride) with cucurbit[7]uril enhances the yield of AAPH-derived radicals
(2023) Forero Girón, Angie; Fuentealba Patiño, Denis Alberto; Mariño Ocampo, Nory Johana; Gutiérrez Oliva, Soledad; Herrera Pisani, Bárbara Andrea; Toro Labbé, Alejandro; Fuentes Lemus, Eduardo; Davies, Michael J.; Aliaga Miranda, Margarita Elly; López Alarcón, Camilo Ignacio
AAPH (2,2′-azobis(2-methylpropionamidine) dihydrochloride), a water-soluble azo compound is widely employed to produce peroxyl radicals for chemical and biological studies. This compound is shown herein to form a stable inclusion complex with cucurbit[7]uril (CB7), a well-established supramolecular host. Competitive binding assays using berberine dye, isothermal titration calorimetry (ITC), and nuclear magnetic resonance (1H-NMR) experiments, provided evidence for the inclusion of AAPH inside the CB7 cavity with a binding constant of 2.5 ± 0.8 x 105 L mol-1 (determined by ITC). Computational analysis at B3LYP-D3BJ/6-311G(d,p) of the complex (AAPH@CB7) showed interactions of the positively-charged amino groups of AAPH with carbonyl functions at the CB7 entrances. Photolysis of AAPH@CB7 by illumination at 365 nm, gave a higher yield of carbon-centered radicals when compared to the absence of CB7, as evidenced by electron paramagnetic resonance spin trapping using α-phenyl-N-t-butylnitrone. Enhanced radical formation was corroborated by increased consumption of pyrogallol red, free Trp and Trp-containing peptides when these were exposed to AAPH@CB7 in the presence of light. The increased yield of radicals generated by AAPH@CB7 is believed to arise from a pull effect of CB7 portals on initial AAPH-derived carbon-centered radicals generated by photolysis. It is proposed that these radicals are exposed and released to the bulk solution and react with O2 to give peroxyl radicals. These results suggest that the AAPH@CB7 complex can be used to generate high yields of peroxyl radicals for their use in studying these species in material, environmental and biomedical sciences amongst others.
Complexes between 2,20-azobis(2methylpropionamidine) dihydrochloride (AAPH) and cucurbit[n]uril hosts modulate the yield and fate of photolytically-generated AAPH radicals
(Royal Society of Chemistry, 2024) Forero Girón, Angie; Oyarzún Alfaro, Mauricio Sebastián; Droguett Muñoz, Kevin Arturo; Fuentealba Patiño, Denis Alberto; Gutiérrez Oliva, Soledad; Herrera Pisani, Bárbara Andrea; Toro Labbé, Alejandro; Fuentes Lemus, Eduardo Felipe; Davies, Michael J.; López Alarcón, Camilo Ignacio; Aliaga Miranda, Margarita Elly
Using theoretical and experimental tools we investigated the recognition of AAPH (2,2′-azobis(2-methylpropionamidine) dihydrochloride), a well-known water-soluble azo-compound employed as a source of peroxyl radicals, by cucurbit[6]uril (CB[6]), and cucurbit[8]uril (CB[8]). Density functional theory calculations and isothermal titration calorimetry experiments demonstrated that AAPH was not included in the cavity of CB[6], however, an exclusion complex was generated. Inclusion of AAPH in the CB[8] cavity was favored, forming stable inclusion complexes at 1 : 1 and 2 : 1 stoichiometries; AAPH@CB[8] and 2AAPH@CB[8], respectively. Radical formation upon photolytic cleavage of AAPH was examined theoretically, and by spin trapping with electron paramagnetic resonance. The radical yields detected with uncomplexed (free) AAPH and the AAPH-CB[6] (exclusion) complex were identical, whereas a marked decrease was shown for AAPH@CB[8]. Lower decreases were seen with a bimolecular (2 : 1) AAPH-CB[8] inclusion complex (2AAPH@CB[8]). This modulation was corroborated by the consumption of pyrogallol red (PGR), an oxidizable dye that does not associate with CB[6] or CB[8]. AAPH-CB[6] and 2AAPH@CB[8] did not significantly modify the initial consumption rate (Ri) of PGR, whereas AAPH@CB[8] decreased this. The oxidative consumption of free Trp, Gly-Trp and Trp-Gly by radicals derived from AAPH in the presence of CB[8] showed a dependence on the association of the targets with CB[8].
Crowding modulates the glycation of plasma proteins: In vitro analysis of structural modifications to albumin and transferrin and identification of sites of modification
(2022) Fuentes Lemus, Eduardo Felipe; Reyes Valenzuela, Juan Sebastián; López Alarcón, Camilo Ignacio; Davies, Michael J.
Protein modification occurs in biological milieus that are characterized by high concentrations of (macro)mol-ecules (i.e. heterogeneous and packed environments). Recent data indicate that crowding can modulate the extent and rate of protein oxidation, however its effect on other post-translational modifications remains to be explored. In this work we hypothesized that crowding would affect the glycation of plasma proteins. Physiologically-relevant concentrations of albumin (35 mg mL-1) and transferrin (2 mg mL-1) were incubated with methylglyoxal and glyoxal (5 mu M-5 mM), two alpha-oxoaldehyde metabolites that are elevated in the plasma of people with diabetes. Crowding was induced by adding dextran or ficoll polymers. Electrophoresis, electron microscopy, fluorescence spectroscopy and mass spectrometry were employed to investigate the structural consequences of glycation under crowded conditions. Our data demonstrate that crowding modulates the extent of formation of transferrin cross-links, and also the modification pathways in both albumin and transferrin. Arginine was the most susceptible residue to modification, with lysine and cysteine also affected. Loss of 0.48 and 7.28 arginine residues per protein molecule were determined on incubation with 500 mu M methylglyoxal for albumin and transferrin, respectively. Crowding did not influence the extent of loss of arginine and lysine for either protein, but the sites of modification, detected by LC-MS, were different between dilute and crowded conditions. These data confirm the relevance of studying modification processes under conditions that closely mimic biological milieus. These data unveil additional factors that influence the pattern and extent of protein modification, and their structural consequences, in biological systems.
Effect of macromolecular crowding on protein oxidation: Consequences on the rate, extent and oxidation pathways
(2021) Fuentes Lemus, Eduardo Felipe; Reyes Valenzuela, Juan Sebastián; Gamon, Luke F.; López Alarcón, Camilo Ignacio; Davies, Michael J.
Biological systems are heterogeneous and crowded environments. Such packed milieus are expected to modulate reactions both inside and outside the cell, including protein oxidation. In this work, we explored the effect of macromolecular crowding on the rate and extent of oxidation of Trp and Tyr, in free amino acids, peptides and proteins. These species were chosen as they are readily oxidized and contribute to damage propagation. Dextran was employed as an inert crowding agent, as this polymer decreases the fraction of volume available to other (macro)molecules. Kinetic analysis demonstrated that dextran enhanced the rate of oxidation of free Trp, and peptide Trp, elicited by AAPH-derived peroxyl radicals. For free Trp, the rates of oxidation were 15.0 ± 2.1 and 30.5 ± 3.4 μM min−1 without and with dextran (60 mg mL−1) respectively. Significant increases were also detected for peptide-incorporated Trp. Dextran increased the extent of Trp consumption (up to 2-fold) and induced short chain reactions. In contrast, Tyr oxidation was not affected by the presence of dextran. Studies on proteins, using SDS-PAGE and LC-MS, indicated that oxidation was also affected by crowding, with enhanced amino acid loss (45% for casein), chain reactions and altered extents of oligomer formation. The overall effects of dextran-mediated crowding were however dependent on the protein structure. Overall, these data indicate that molecular crowding, as commonly encountered in biological systems affect the rates, and extents of oxidation, and particularly of Trp residues, illustrating the importance of appropriate choice of in vitro systems to study biological oxidations.
Implications of differential peroxyl radical-induced inactivation of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase for the pentose phosphate pathway
(Nature Research, 2022) Reyes Valenzuela, Juan Sebastián; Figueroa Alegría, Juan David; Martínez Rojas, Francisco Javier; López Alarcon, Camilo Ignacio; Fuentes Lemus, Eduardo Felipe; Hagglund, P.M.; Davies, Michael J.; Fierro Huerta, Angelica María; Arenas, Felipe
© 2022, The Author(s).Escherichia coli glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) are key enzymes of the pentose phosphate pathway, responsible for the NADPH production in cells. We investigated modification of both enzymes mediated by peroxyl radicals (ROO·) to determine their respective susceptibilities to and mechanisms of oxidation. G6PDH and 6PGDH were incubated with AAPH (2,2?-azobis(2-methylpropionamidine)dihydrochloride), which was employed as ROO· source. The enzymatic activities of both enzymes were determined by NADPH release, with oxidative modifications examined by electrophoresis and liquid chromatography (LC) with fluorescence and mass (MS) detection. The activity of G6PDH decreased up to 62.0 ± 15.0% after 180 min incubation with 100 mM AAPH, whilst almost total inactivation of 6PGDH was determined under the same conditions. Although both proteins contain abundant Tyr (particularly 6PGDH), these residues were minimally affected by ROO·, with Trp and Met being major targets. LC–MS and in silico analysis showed that the modification sites of G6PDH are distant to the active site, consistent with a dispersed distribution of modifications, and inactivation resulting from oxidation of multiple Trp and Met residues. In contrast, the sites of oxidation detected on 6PGDH are located close to its catalytic site indicating a more localized oxidation, and a consequent high susceptibility to ROO·-mediated inactivation.
M. jannaschii FtsZ, a key protein in bacterial cell division, is inactivated by peroxyl radical-mediated methionine oxidation
(Elsevier, 2021) Reyes Valenzuela, Juan Sebastian; Fuentes-Lemus, Eduardo; Aspée, Alexis; Davies, Michael J.; Monasterio, Octavio; López Alarcón, Camilo Ignacio
Oxidation and inactivation of FtsZ is of interest due to the key role of this protein in bacterial cell division. In the present work, we studied peroxyl radical (from AAPH, 2,2′-azobis(2-methylpropionamidine)dihydrochloride) mediated oxidation of the highly stable FtsZ protein (MjFtsZ) from M. jannaschii, a thermophilic microorganism. MjFtsZ contains eleven Met, and single Tyr and Trp residues which would be expected to be susceptible to oxidation. We hypothesized that exposure of MjFtsZ to AAPH-derived radicals would induce Met oxidation, and cross-linking (via di-Tyr and di-Trp formation), with concomitant loss of its functional polymerization and depolymerization (GTPase) activities. Solutions containing MjFtsZ and AAPH (10 or 100 mM) were incubated at 37 °C for 3 h. Polymerization/depolymerization were assessed by light scattering, while changes in mass were analyzed by SDS-PAGE. Amino acid consumption was quantified by HPLC with fluorescence detection, or direct fluorescence (Trp). Oxidation products and modifications at individual Met residues were quantified by UPLC with mass detection. Oxidation inhibited polymerization-depolymerization activity, and yielded low levels of irreversible protein dimers. With 10 mM AAPH only Trp and Met were consumed giving di-alcohols, kynurenine and di-Trp (from Trp) and the sulfoxide (from Met). With 100 mM AAPH low levels of Tyr oxidation (but not di-Tyr formation) were also observed. Correlation with the functional analyses indicates that Met oxidation, and particularly Met164 is the key driver of MjFtsZ inactivation, probably as a result of the position of this residue at the protein-protein interface of longitudinal interactions and in close proximity to the GTP binding site.
Macromolecular crowding and bicarbonate enhance the hydrogen peroxide-induced inactivation of glyceraldehyde-3-phosphate dehydrogenase
(Portland Press LTD, 2024) Bloemen, Rebeca H. J.; Radi, Rafael; Davies, Michael J.; Fuentes Lemus Eduardo Felipe
The active site Cys residue in glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is sensitive to oxidation by hydrogen peroxide (H2O2), with this resulting in enzyme inactivation. This re-routes the carbon flux from glycolysis to the pentose phosphate pathway favoring the formation of NADPH and synthetic intermediates required for antioxidant defense and repair systems. Consequently, GAPDH inactivation serves as a redox switch for metabolic adaptation under conditions of oxidative stress. However, there is a major knowledge gap as to how GAPDH is efficiently oxidized and inactivated, when the increase in intracellular H2O2 is modest, and there is a high concentration of alternative (non-signaling) thiols and efficient peroxide removing systems. We have therefore explored whether GAPDH inactivation is enhanced by two factors of in vivo relevance: macromolecular crowding, an inherent property of biological environments, and the presence of bicarbonate, an abundant biological buffer. Bicarbonate is already known to modulate H2O2 metabolism via formation of peroxymonocarbonate. GAPDH activity was assessed in experiments with low doses of H2O2 under both dilute and crowded conditions (induced by inert high molecular mass polymers and small molecules), in both the absence and presence of 25 mM sodium bicarbonate. H2O2-induced inactivation of GAPDH was observed to be significantly enhanced under macromolecular crowding conditions, with bicarbonate having an additional effect. These data strongly suggest that these two factors are of major importance in redox switch mechanisms involving GAPDH (and possibly other thiol-dependent systems) within the cellular environment.
Oxidation of lysozyme induced by peroxyl radicals involves amino acid modifications, loss of activity, and formation of specific crosslinks
(2021) Fuentes Lemus, Eduardo Felipe; Mariotti, Michele; Hägglund, Per; Leinisch, Fabian; Fierro Huerta, Angélica; Silva Stevens, Eduardo Andrés; Davies, Michael J.; López Alarcón, Camilo Ignacio
The present work examined the oxidation and crosslinking of the anti-bacterial enzyme lysozyme (Lyso), which is present in multiple biological fluids, and released from the cytoplasmic granules of macrophages and neutrophils at sites of infection and inflammation. It is therefore widely exposed to oxidants including peroxyl radicals (ROO?). We hypothesized that exposure to ROO? would generate specific modifications and inter- and intraprotein crosslinks via radical-radical reactions. Lyso was incubated with AAPH (2,2?-azobis(2-methylpropionamidine) dihydrochloride) as a ROO? source. Enzymatic activity was assessed, while oxidative modifications were detected and quantified using electrophoresis and liquid chromatography (UPLC) with fluorescence or mass detection (MS). Computational models of AAPH-Lyso interactions were developed. Exposure of Lyso to AAPH (10 and 100 mM for 3 h, and 20 mM for 1 h), at 37 ?C, decreased enzymatic activity. 20 mM AAPH showed the highest efficiency of Lyso inactivation (1.78 mol of Lyso inactivated per ROO?). Conversion of Met to its sulfoxide, and to a lesser extent, Tyr oxidation to 3,4-dihydroxyphenylalanine and diTyr, were detected by UPLCMS. Extensive transformation of Trp, involving short chain reactions, to kynurenine, oxindole, hydroxytryptophan, hydroperoxides or di-alcohols, and N-formyl-kynurenine was detected, with Trp62, Trp63 and Trp108 the most affected residues. Interactions of AAPH inside the negatively-charged catalytic pocket of Lyso, with Trp108, Asp52, and Glu35, suggest that Trp108 oxidation mediates, at least partly, Lyso inactivation. Crosslinks between Tyr20-Tyr23 (intra-molecular), and Trp62-Tyr23 (inter-molecular), were detected with both proximity (Tyr20-Tyr23), and chain flexibility (Trp62) appearing to favor the formation of covalent crosslinks.
Oxidative Crosslinking of Peptides and Proteins: Mechanisms of Formation, Detection, Characterization and Quantification
(2022) Fuentes Lemus, Eduardo Felipe; Hägglund, Per; López Alarcón, Camilo Ignacio; Davies, Michael J.
Covalent crosslinks within or between proteins play a key role in determining the structure and function of proteins. Some of these are formed intentionally by either enzymatic or molecular reactions and are critical to normal physiological function. Others are generated as a consequence of exposure to oxidants (radicals, excited states or two-electron species) and other endogenous or external stimuli, or as a result of the actions of a number of enzymes (e.g., oxidases and peroxidases). Increasing evidence indicates that the accumulation of unwanted crosslinks, as is seen in ageing and multiple pathologies, has adverse effects on biological function. In this article, we review the spectrum of crosslinks, both reducible and non-reducible, currently known to be formed on proteins; the mechanisms of their formation; and experimental approaches to the detection, identification and characterization of these species.
Peroxyl radical- and photo-oxidation of glucose 6-phosphate dehydrogenase generates cross-links and functional changes via oxidation of tyrosine and tryptophan residues
(2017) Leinisch, Fabian; Mariotti, Michele; Rykaer, Martin; López Alarcón, Camilo Ignacio; Davies, Michael J.; Hagglund, Per
Peroxyl radicals modify 6-phosphogluconolactonase from Escherichia coli via oxidation of specific amino acids and aggregation which inhibits enzyme activity
(ELSEVIER SCIENCE INC, 2023) Reyes Valenzuela, Juan Sebastián; Fuentes Lemus, Eduardo Felipe; Romero, Jefferson; Arenas, Felipe; Fierro Huerta, Angelica María; Davies, Michael J.; Lopez Alarcon Camilo Ignacio
6-phosphogluconolactonase (6PGL) catalyzes the second reaction of the pentose phosphate pathway (PPP) converting 6-phosphogluconolactone to 6-phosphogluconate. The PPP is critical to the generation of NADPH and metabolic intermediates, but some of its components are susceptible to oxidative inactivation. Previous studies have characterized damage to the first (glucose-6-phosphate dehydrogenase) and third (6-phosphogluconate dehydrogenase) enzymes of the pathway, but no data are available for 6PGL. This knowledge gap is addressed here. Oxidation of Escherichia coli 6PGL by peroxyl radicals (ROO center dot, from AAPH (2,2 '-azobis(2-methylpropionamidine) dihydrochloride) was examined using SDS-PAGE, amino acid consumption, liquid chromatography with mass detection (LC-MS), protein carbonyl formation and computational methods. NADPH generation was assessed using mixtures all three enzymes of the oxidative phase of the PPP. Incubation of 6PGL with 10 or 100 mM AAPH resulted in protein aggregation mostly due to reducible (disulfide) bonds. High fluxes of ROO center dot induced consumption of Cys, Met and Trp, with the Cys oxidation rationalizing the aggregate formation. Low levels of carbonyls were detected, while LC-MS analyses provided evidence for oxidation of selected Trp and Met residues (Met1, Trp18, Met41, Trp203, Met220 and Met221). ROO center dot elicited little loss of enzymatic activity of monomeric 6PGL, but the aggregates showed diminished NADPH generation. This is consistent with in silico analyses that indicate that the modified Trp and Met are far from the 6-phosphogluconolactone binding site and the catalytic dyad (His130 and Arg179). Together these data indicate that monomeric 6PGL is a robust enzyme towards oxidative inactivation by ROO center dot and when compared to other PPP enzymes.
Quantification of carbonate radical formation by the bicarbonate-dependent peroxidase activity of superoxide dismutase 1 using pyrogallol red bleaching
(2019) Figueroa Alegría, Juan David; Fuentes Lemus, Eduardo Felipe; Dorta Pérez, Eva; Melin, Victoria; Cortés Ríos, Javiera Alejandra; Faúndez Cáceres, Mario; Contreras, David; Denicola, Ana; Álvarez, Beatriz; Davies, Michael J.; López Alarcón, Camilo Ignacio
Carbonate radicals (CO3radical dot-) are generated by the bicarbonate-dependent peroxidase activity of cytosolic superoxide dismutase (Cu,Zn-SOD, SOD-1). The present work explored the use of bleaching of pyrogallol red (PGR) dye to quantify the rate of CO3radical dot- formation from bovine and human SOD-1 (bSOD-1 and hSOD-1, respectively). This approach was compared to previously reported methods using electron paramagnetic resonance spin trapping with DMPO, and the oxidation of ABTS (2,2-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid). The kinetics of PGR consumption elicited by CO3radical dot- was followed by visible spectrophotometry. Solutions containing PGR (5–200 μM), SOD-1 (0.3–3 μM), H2O2 (2 mM) in bicarbonate buffer (200 mM, pH 7.4) showed a rapid loss of the PGR absorption band centered at 540 nm. The initial consumption rate (Ri) gave values independent of the initial PGR concentration allowing an estimate to be made of the rate of CO3radical dot- release of 24.6 ± 4.3 μM min−1 for 3 μM bSOD-1. Both bSOD-1 and hSOD-1 showed a similar peroxidase activity, with enzymatic inactivation occurring over a period of 20 min. The single Trp residue (Trp32) present in hSOD-1 was rapidly consumed (initial consumption rate 1.2 ± 0.1 μM min−1) with this occurring more rapidly than hSOD-1 inactivation, suggesting that these processes are not directly related. Added free Trp was rapidly oxidized in competition with PGR. These data indicate that PGR reacts rapidly and efficiently with CO3radical dot- resulting from the peroxidase activity of SOD-1, and that PGR-bleaching is a simple, fast and cheap method to quantify CO3radical dot- release from bSOD-1 and hSOD-1 peroxidase activity.
Riboflavin-induced Type 1 photo-oxidation of tryptophan using a high intensity 365 nm light emitting diode
(2019) Silva, Eduardo; Barrias, Pablo; Fuentes Lemus, Eduardo Felipe; Tirapegui, Cristian; Aspee, Alexis; Carroll, Luke; Davies, Michael J.; López Alarcón, Camilo Ignacio
Role of amino acid oxidation and protein unfolding in peroxyl radical and peroxynitrite-induced inactivation of glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides
(2022) Figueroa Alegría, Juan David; Fuentes Lemus, Eduardo Felipe; Reyes Valenzuela, Juan Sebastián; Loaiza Hernández, Matías Ignacio; Aliaga Miranda, Margarita Elly; Fierro Huerta, Angélica; Leinisch, Fabian; Hagglund, Per; Davies, Michael J.; López Alarcón, Camilo Ignacio
The mechanisms underlying the inactivation of Leuconostoc mesenteroides glucose 6-phosphate dehydrogenase (G6PDH) induced by peroxyl radicals (ROO center dot) and peroxynitrite (ONOO-), were explored. G6PDH was incubated with AAPH (2,2'-azobis(2-methylpropionamidine)dihydrochloride), used as ROO center dot source, and ONOO-. Enzymatic activity was assessed by NADPH generation, while oxidative modifications were analyzed by gel electrophoresis and liquid chromatography (LC) with fluorescence and mass detection. Changes in protein conformation were studied by circular dichroism (CD) and binding of the fluorescent dye ANS (1-anilinonaph-thalene-8-sulfonic acid). Incubation of G6PDH (54.4 mu M) with 60 mM AAPH showed an initial phase without significant changes in enzymatic activity, followed by a secondary time-dependent continuous decrease in activity to similar to 59% of the initial level after 90 min. ONOO- induced a significant and concentration-dependent loss of G6PDH activity with similar to 46% of the initial activity lost on treatment with 1.5 mM ONOO-. CD and ANS fluorescence indicated changes in G6PDH secondary structure with exposure of hydrophobic sites on exposure to ROO center dot, but not ONOO-. LC-MS analysis provided evidence for ONOO--mediated oxidation of Tyr, Met and Trp residues, with damage to critical Met and Tyr residues underlying enzyme inactivation, but without effects on the native (dimeric) state of the protein. In contrast, studies using chloramine T, a specific oxidant of Met, provided evidence that oxidation of specific Met and Trp residues and concomitant protein unfolding, loss of dimer structure and protein aggregation are involved in G6PDH inactivation by ROO center dot. These two oxidant systems therefore have markedly different effects on G6PDH structure and activity.
The enzymes of the oxidative phase of the pentose phosphate pathway as targets of reactive species: consequences for NADPH production
(2023) Fuentes Lemus, Eduardo Felipe; Reyes Valenzuela, Juan Sebastián; Figueroa Alegría, Juan David; Davies, Michael J.; López Alarcón, Camilo Ignacio
The pentose phosphate pathway (PPP) is a key metabolic pathway. The oxidative phase of this process involves three reactions catalyzed by glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconolactonase (6PGL) and 6-phosphogluconate dehydrogenase (6PGDH) enzymes. The first and third steps (catalyzed by G6PDH and 6PGDH, respectively) are responsible for generating reduced nicotinamide adenine dinucleotide phosphate (NAPDH), a key cofactor for maintaining the reducing power of cells and detoxification of both endogenous and exogenous oxidants and electrophiles. Despite the importance of these enzymes, little attention has been paid to the fact that these proteins are targets of oxidants. In response to oxidative stimuli metabolic pathways are modulated, with the PPP often up-regulated in order to enhance or maintain the reductive capacity of cells. Under such circumstances, oxidation and inactivation of the PPP enzymes could be detrimental. Damage to the PPP enzymes may result in a downward spiral, as depending on the extent and sites of modification, these alterations may result in a loss of enzymatic activity and therefore increased oxidative damage due to NADPH depletion. In recent years, it has become evident that the three enzymes of the oxidative phase of the PPP have different susceptibilities to inactivation on exposure to different oxidants. In this review, we discuss existing knowledge on the role that these enzymes play in the metabolism of cells, and their susceptibility to oxidation and inactivation with special emphasis on NADPH production. Perspectives on achieving a better understanding of the molecular basis of the oxidation these enzymes within cellular environments are given.

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