Characterisation of the non-oxidative degradation pathway of dehydroascorbic acid in slightly acidic aqueous solution

Dewhirst, Rebecca A.; Murray, Lorna; Mackay, C. Logan; Sadler, Ian H.; Fry, Stephen C.

doi:10.1016/j.abb.2019.108240

Cited by 8 publications

(7 citation statements)

References 33 publications

(47 reference statements)

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“…It has previously been demonstrated that DHA spontaneously converts to 2,3-diketo-L-gulonic acid (DKG) [61][62][63] in aqueous solutions. DKG is known to undergo additional transformations in solution giving rise to various compounds, some of which are known to be redox-active [64,65]. Importantly, one such DKG derivative (called 'compound 1') has been isolated by HPLC and shown to be capable of inducing nonenzymatic hydrogen peroxide production, which is a relevant feature in the context of LPMO catalysis [64].…”

Section: The Accumulation Of Dha Derivatives In the Presence And Absence Of Lpmomentioning

confidence: 99%

The impact of reductants on the catalytic efficiency of a lytic polysaccharide monooxygenase and the special role of dehydroascorbic acid

et al. 2021

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Monocopper lytic polysaccharide monooxygenases (LPMOs) catalyse oxidative cleavage of glycosidic bonds in a reductant-dependent reaction.Recent studies indicate that LPMOs, rather than being O 2 -dependent monooxygenases, are H 2 O 2 -dependent peroxygenases. Here, we describe SscLPMO10B, a novel LPMO from the phytopathogenic bacterium Streptomyces scabies and address links between this enzyme's catalytic rate and in situ hydrogen peroxide production in the presence of ascorbic acid, gallic acid and L-cysteine. Studies of Avicel degradation showed a clear correlation between the catalytic rate of SscLPMO10B and the rate of H 2 O 2 generation in the reaction mixture. We also assessed the impact of oxidised ascorbic acid, dehydroascorbic acid (DHA), on LPMO activity, since DHA, which is not considered a reductant, was recently reported to drive LPMO reactions. Kinetic studies, combined with NMR analysis, showed that DHA is unstable and converts into multiple derivatives, some of which are redox active and can fuel the LPMO reaction by reducing the active site copper and promoting H 2 O 2 production. These results show that the apparent monooxygenase activity observed in SscLPMO10B reactions without exogenously added H 2 O 2 reflects a peroxygenase reaction.

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Section: The Accumulation Of Dha Derivatives In the Presence And Absence Of Lpmomentioning

confidence: 99%

The impact of reductants on the catalytic efficiency of a lytic polysaccharide monooxygenase and the special role of dehydroascorbic acid

et al. 2021

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“…Of note, it cannot be excluded that absorbance from ascorbic acid oxidation products also influences the peak maximum at ∼233 nm. Ascorbic acid is initially oxidized to dehydroascorbic acid, , which is rapidly degraded into a plethora of oxidation products, , all of which could potentially influence the CD spectra to a variable degree.…”

Section: Discussionmentioning

confidence: 99%

Following the Fate of Lytic Polysaccharide Monooxygenases under Oxidative Conditions by NMR Spectroscopy

et al. 2023

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Lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that catalyze oxidative cleavage of polysaccharides, such as cellulose and chitin. LPMO catalysis requires a reductant, such as ascorbic acid, and hydrogen peroxide, which can be generated in situ in the presence of molecular oxygen and various electron donors. While it is known that reduced LPMOs are prone to autocatalytic oxidative damage due to offpathway reactions with the oxygen co-substrate, little is known about the structural consequences of such damage. Here, we present atomic-level insights into how the structure of the chitinactive SmLPMO10A is affected by oxidative damage using NMR and circular dichroism spectroscopy. Incubation with ascorbic acid could lead to rearrangements of aromatic residues, followed by more profound structural changes near the copper-active site and loss of activity. Longer incubation times induced changes in larger parts of the structure, indicative of progressing oxidative damage. Incubation with ascorbic acid in the presence of chitin led to similar changes in the observable (i.e., not substrate-bound) fraction of the enzyme. Upon subsequent addition of H 2 O 2 , which drastically speeds up chitin hydrolysis, NMR signals corresponding to seemingly intact SmLPMO10A reappeared, indicating dissociation of catalytically competent LPMO. Activity assays confirmed that SmLPMO10A retained catalytic activity when preincubated with chitin before being subjected to conditions that induce oxidative damage. Overall, this study provides structural insights into the process of oxidative damage of SmLPMO10A and demonstrates the protective effect of the substrate.

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“…Among these products, some may delay APXs action and inhibit ROS scavenging. Moreover, some products, such as 2,3-diketogulonate, produce H 2 O 2 by AOs or non-enzymatical pathway (Parsons and Fry, 2012;Kärkönen et al, 2017;Dewhirst and Fry, 2018;Smirnoff, 2018;Dewhirst et al, 2020). Therefore, unlike APXs, which use ASC to scavenge ROS and eliminate oxidative damage, AOs consume ASC to accelerate the accumulation of ROS in apoplast.…”

Section: As a Regulator Asc Manipulates Stress Signal Transduction And Coordinates Abiotic Stress Responsesmentioning

confidence: 99%

The Multiple Roles of Ascorbate in the Abiotic Stress Response of Plants: Antioxidant, Cofactor, and Regulator

Xiao

Zhu

et al. 2021

Front. Plant Sci.

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Ascorbate (ASC) plays a critical role in plant stress response. The antioxidant role of ASC has been well-studied, but there are still several confusing questions about the function of ASC in plant abiotic stress response. ASC can scavenge reactive oxygen species (ROS) and should be helpful for plant stress tolerance. But in some cases, increasing ASC content impairs plant abiotic stress tolerance, whereas, inhibiting ASC synthesis or regeneration enhances plant stress tolerance. This confusing phenomenon indicates that ASC may have multiple roles in plant abiotic stress response not just as an antioxidant, though many studies more or less ignored other roles of ASC in plant. In fact, ACS also can act as the cofactor of some enzymes, which are involved in the synthesis, metabolism, and modification of a variety of substances, which has important effects on plant stress response. In addition, ASC can monitor and effectively regulate cell redox status. Therefore, we believe that ASC has atleast triple roles in plant abiotic stress response: as the antioxidant to scavenge accumulated ROS, as the cofactor to involve in plant metabolism, or as the regulator to coordinate the actions of various signal pathways under abiotic stress. The role of ASC in plant abiotic stress response is important and complex. The detail role of ASC in plant abiotic stress response should be analyzed according to specific physiological process in specific organ. In this review, we discuss the versatile roles of ASC in the response of plants to abiotic stresses.

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Characterisation of the non-oxidative degradation pathway of dehydroascorbic acid in slightly acidic aqueous solution

Cited by 8 publications

References 33 publications

The impact of reductants on the catalytic efficiency of a lytic polysaccharide monooxygenase and the special role of dehydroascorbic acid

The impact of reductants on the catalytic efficiency of a lytic polysaccharide monooxygenase and the special role of dehydroascorbic acid

Following the Fate of Lytic Polysaccharide Monooxygenases under Oxidative Conditions by NMR Spectroscopy

The Multiple Roles of Ascorbate in the Abiotic Stress Response of Plants: Antioxidant, Cofactor, and Regulator

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