Oxygen dependency of one-electron reactions generating ascorbate radicals and hydrogen peroxide from ascorbic acid

Boatright, W.L.

doi:10.1016/j.foodchem.2015.07.141

Cited by 54 publications

(37 citation statements)

References 41 publications

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“…Recently, it has been shown that small amounts of H 2 O 2 boost LPMO activity, while higher amounts lead to inactivation of the enzyme . The presence of ascorbic acid in the reactions described above will lead to generation of H 2 O 2 , which perhaps could explain the observed apparent enzyme inactivation. It was also shown that inactivation of LPMOs by excess H 2 O 2 is accompanied by oxidative damage in the catalytic center only, with the N‐terminal histidine being especially vulnerable.…”

Section: Discussionmentioning

confidence: 99%

Methylation of the N‐terminal histidine protects a lytic polysaccharide monooxygenase from auto‐oxidative inactivation

et al. 2018

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The catalytically crucial N-terminal histidine (His1) of fungal lytic polysaccharide monooxygenases (LPMOs) is post-translationally modified to carry a methylation. The functional role of this methylation remains unknown. We have carried out an in-depth functional comparison of two variants of a family AA9 LPMO from Thermoascus aurantiacus (TaLPMO9A), one with, and one without the methylation on His1. Various activity assays showed that the two enzyme variants are identical in terms of substrate preferences, cleavage specificities and the ability to activate molecular oxygen. During the course of this work, new functional features of TaLPMO9A were discovered, in particular the ability to cleave xyloglucan, and these features were identical for both variants. Using a variety of techniques, we further found that methylation has minimal effects on the pK of His1, the affinity for copper and the redox potential of bound copper. The two LPMOs did, however, show clear differences in their resistance against oxidative damage. Studies with added hydrogen peroxide confirmed recent claims that low concentrations of H O boost LPMO activity, whereas excess H O leads to LPMO inactivation. The methylated variant of TaLPMO9A, produced in Aspergillus oryzae, was more resistant to excess H O and showed better process performance when using conditions that promote generation of reactive-oxygen species. LPMOs need to protect themselves from reactive oxygen species generated in their active sites and this study shows that methylation of the fully conserved N-terminal histidine provides such protection.

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Section: Discussionmentioning

confidence: 99%

Methylation of the N‐terminal histidine protects a lytic polysaccharide monooxygenase from auto‐oxidative inactivation

et al. 2018

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“…For example, the formation of H 2 O 2 in the reaction between AscA and molecular oxygen is well-known (35). Furthermore, the oxidation of AscA by O 2 is catalyzed by metal ions, like Cu(II) (36,37), so that their presence even in trace amounts can significantly affect the formation of H 2 O 2 and interpretation of the results of LPMO kinetics. The problem is further amplified by the occurrence of metal ions in polymeric substrates of LPMOs, such as cellulose and chitin (38 -40).…”

Section: Experimental Set-upmentioning

confidence: 99%

Kinetic insights into the role of the reductant in H2O2-driven degradation of chitin by a bacterial lytic polysaccharide monooxygenase

Kuusk

Kont

Kuusk

et al. 2019

Journal of Biological Chemistry

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“…Their combination appeared to be crucial. A marked protective effect, when oxygen is replaced by argon in a solution containing Cu 2þ ions, was also observed by Boatright (2016). Subsequently, the effect of oxygen deprivation was assessed in the supernatant of centrifuged apple pur ee.…”

Section: Anaerobic Vs Aerobic Degradationmentioning

confidence: 93%

“…However, it is not known if the concomitant presence of oxygen is necessary for the Fe 3þ ion-caused oxidation. Under anaerobic conditions and in the presence of Cu 2þ ions, the stability of ascorbic acid can almost completely be preserved in contrast to aerobic conditions where ascorbic acid degrades rapidly (Boatright, 2016). The aim of the present study was to reveal oxygen availabilities in different media during heat treatment at 80 C and to understand the influence of Fe 3þ ions, ascorbic acid concentrations and temperature.…”

Section: Introductionmentioning

confidence: 96%

“…This seems to result from of a redox reaction with ascorbic acid being oxidized and Fe 3þ ions being reduced to Fe 2þ ions. Fe 2þ ions, in turn, react in the Fenton reaction with hydrogen peroxide (Choe & Min, 2005) which is formed during the oxidation of ascorbic acid (Boatright, 2016). However, it is not known if the concomitant presence of oxygen is necessary for the Fe 3þ ion-caused oxidation.…”

Section: Introductionmentioning

confidence: 99%

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Oxygen availability in model solutions and purées during heat treatment and the impact on vitamin C degradation

Herbig

Maingonnat

Renard

2017

LWT - Food Science and Technology

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a b s t r a c tOxygen availability in different media during heat treatment (8 h at 80 C) and the related vitamin C loss was assessed. Dissolved oxygen in water containing 3 mmol kg À1 of ascorbic acid decreased initially and seemed to be replaced by oxygen from the headspace in the course of time, as oxygen values increased again. In apple pur ee and carrot pur ee in contrast, oxygen was depleted within 60 min. Vitamin C in ultrapure water was stable even in the presence of oxygen. A trigger seemed to be crucial to launch vitamin C degradation. Fe 3þ ions added to water, but also the media Mc Ilvaine citrate-phosphate buffer (pH 3.5) or apple pur ee, initiated degradation. Adding Fe 3þ ions to apple pur ee did not accelerate vitamin C degradation but shifted the equilibrium between ascorbic acid and dehydroascorbic acid to the latter. Oxygen deprivation stabilized completely vitamin C, independently of the medium tested. A temperature decrease to 70 or 60 C, in contrast, had no effect on the degradation extent of vitamin C in water containing 20 mmol kg À1 Fe 3þ ions but led to complete stability in apple pur ee.

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Oxygen dependency of one-electron reactions generating ascorbate radicals and hydrogen peroxide from ascorbic acid

Cited by 54 publications

References 41 publications

Methylation of the N‐terminal histidine protects a lytic polysaccharide monooxygenase from auto‐oxidative inactivation

Methylation of the N‐terminal histidine protects a lytic polysaccharide monooxygenase from auto‐oxidative inactivation

Kinetic insights into the role of the reductant in H2O2-driven degradation of chitin by a bacterial lytic polysaccharide monooxygenase

Oxygen availability in model solutions and purées during heat treatment and the impact on vitamin C degradation

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