Dual Roles of Dissolved Organic Matter as Sensitizer and Quencher in the Photooxidation of Tryptophan

Janssen, Elisabeth M.-L.; Erickson, Paul R.; McNeill, Kristopher

doi:10.1021/es500535a

Cited by 170 publications

(176 citation statements)

References 36 publications

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“…These observations may seem unexpected if one considers DOM as only a photosensitizer producing 3 DOM and reactive oxygen species. However, the reduced inactivation rate constants can be rationalized when considering DOM as a quencher of photooxidation 11,17,18 and specifically of tryptophan photooxidation ( Figure 3). 11 As previously established, free tryptophan reacts to a radical cation intermediate by direct 19,20 and indirect photochemical reactions with excited triplet-state DOM ( 3 DOM).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…However, the reduced inactivation rate constants can be rationalized when considering DOM as a quencher of photooxidation 11,17,18 and specifically of tryptophan photooxidation ( Figure 3). 11 As previously established, free tryptophan reacts to a radical cation intermediate by direct 19,20 and indirect photochemical reactions with excited triplet-state DOM ( 3 DOM). 11 Suitable electron donors, i.e., antioxidants, can convert that radical cation back to tryptophan and hence quench these two photodegradation pathways (Figure 3).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…11 Suitable electron donors, i.e., antioxidants, can convert that radical cation back to tryptophan and hence quench these two photodegradation pathways (Figure 3). 11,21,22 We recently demonstrated that redox-active DOM can act as an antioxidant toward photooxidation of monomeric tryptophan. 11 These quenchable pathways of direct photolysis and reaction with 3 DOM accounted for 80% of tryptophan decay during sunlight exposure with 5 mg C L −1 DOM concentration.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…11,21,22 We recently demonstrated that redox-active DOM can act as an antioxidant toward photooxidation of monomeric tryptophan. 11 These quenchable pathways of direct photolysis and reaction with 3 DOM accounted for 80% of tryptophan decay during sunlight exposure with 5 mg C L −1 DOM concentration. 11 We further investigated the involvement of photooxidation of tryptophan residues in the three-dimensional structure of phosphatase by following changes in tryptophan-like fluorescence and comparing these to inactivation rates.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…We previously demonstrated that DOM plays dual roles in the photodegradation of monomeric tryptophan acting as a sensitizer and quencher. 11 Direct photoreaction of tryptophan as well as reaction of tryptophan with excited triplet-state DOM form an intermediate tryptophan radical cation, which can be converted back to tryptophan by suitable electron or hydrogen atom donors. With a better mechanistic understanding of tryptophan's aquatic photochemistry, the question arises whether DOM can similarly affect the photodegradation of tryptophan residues within biomacromolecular structures of proteins.…”

Section: ■ Introductionmentioning

confidence: 99%

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Environmental Photoinactivation of Extracellular Phosphatases and the Effects of Dissolved Organic Matter

Janssen

McNeill

2014

Environ. Sci. Technol.

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Alkaline phosphatases are ubiquitous extracellular enzymes in aquatic systems and play a central role in the biogeochemical cycling of phosphorus. Yet, the photochemical stability of phosphatase and effects of natural organic matter (DOM) are not completely understood. We demonstrate that phosphatase activity in natural biofilm samples decreased during sunlight exposure similar to well-defined bacterial phosphatase solutions. Direct photoinactivation was slowed by more than 50% in the presence of redox-active dissolved organic matter (DOM, 10 mgC L(–1)) or a model antioxidant (esculetin, 50 μM), even after light screening effects had been accounted for. Thus, DOM can not only inhibit enzymes (in the dark) or sensitize photodegradation by producing photochemically produced reactive intermediates but can also significantly quench direct photoinactivation of phosphatase. Our data further suggest that direct photooxidation of tryptophan residues within the protein structure are significantly involved in the photoinactivation of phosphatase because a loss of tryptophan-like fluorescence paralleled photoinactivation kinetics and because DOM acted as an antioxidant toward photoinactivation, a phenomenon recently established for the photooxidation of freely dissolved tryptophan. Thus, photoinactivation of phosphatase can be significantly slowed in the presence of naturally occurring antioxidants like DOM. The mechanistic link between tryptophan photooxidation and inactivation of phosphatase may have applicability to other extracellular enzymes but remains to be established.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Environmental Photoinactivation of Extracellular Phosphatases and the Effects of Dissolved Organic Matter

Janssen

McNeill

2014

Environ. Sci. Technol.

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Photodegradation disproportionately impacts biodegradation of semi‐labile DOM in streams

Bowen

Kaplan

Cory

2019

Limnology & Oceanography

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Exposure of dissolved organic matter (DOM) to sunlight can increase or decrease the fraction that is biodegradable (BDOM), but conceptual models fail to explain this dichotomy. We investigated the effect of sunlight exposure on BDOM, addressing three knowledge gaps: (1) how fractions of DOM overlap in their susceptibility to degradation by sunlight and microbes, (2) how the net effect of sunlight on BDOM changes with photon dose, and (3) how rates of DOM photodegradation and biodegradation compare in a stream. Stream waters were exposed to sunlight, and then fed through bioreactors designed to separate labile and semi‐labile pools within BDOM. The net effects of photodegradation on DOM biodegradability, while generally positive, represented the balance between photochemical production and removal of BDOM that was mediated by photon dose. By using sunlight exposure times representative of sunlight exposures in a headwater stream and bioreactors colonized with natural communities and scaled to whole‐stream dynamics, we were able to relate our laboratory findings to the stream. The impact of sunlight exposure on rates of DOM biodegradation in streams was calculated using rates of light absorption by chromophoric DOM, apparent quantum yields for photomineralization and photochemical alteration of BDOM, and mass transfer coefficients for labile and semi‐labile DOM. Rates of photochemical alteration of labile DOM were an order of magnitude lower than rates of biodegradation of labile DOM, but for semi‐labile DOM, these rates were similar, suggesting that sunlight plays a substantial role in the fate of semi‐labile DOM in streams.

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Photochemical degradation of imazosulfuron under simulated California rice field conditions

Rering

Gonzalez

Keener

et al. 2015

Pest Management Science

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Aqueous photolysis is predicted to be an important process in the overall degradation of IMZ in the environment, regardless of variances in salinity, organic matter and temperature. Based on the predicted half-life of IMZ in a California rice field (3.6 days), state-mandated holding periods for field water post-IMZ application (30 days) are expected to allow for sufficient clearance of the herbicide (>98%), preventing significant contamination of the environment upon release of tailwater. © 2015 Society of Chemical Industry.

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Dual Roles of Dissolved Organic Matter as Sensitizer and Quencher in the Photooxidation of Tryptophan

Cited by 170 publications

References 36 publications

Environmental Photoinactivation of Extracellular Phosphatases and the Effects of Dissolved Organic Matter

Environmental Photoinactivation of Extracellular Phosphatases and the Effects of Dissolved Organic Matter

Photodegradation disproportionately impacts biodegradation of semi‐labile DOM in streams

Photochemical degradation of imazosulfuron under simulated California rice field conditions

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