The photochemical degradation of cystine in aqueous solutions in the presence of nitrogen

Asquith, R. S.; Shah, Ansuya V.

doi:10.1016/0304-4165(71)90071-7

Cited by 10 publications

(9 citation statements)

References 23 publications

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“…Photolysis of cystine may also occur in the absence of aromatic amino acids and leads to degradation both in the presence and in the absence of air . In the presence of oxygen, degradation of cystine occurs only when the incident irradiation wavelength is below 300 nm in a reaction in which the quantum yield for the destruction of cystine is pH-independent . Direct photolysis of cystine results mainly in S–S cleavage and with only minor degradation through C–S cleavage .…”

Section: Introductionmentioning

confidence: 99%

“…Direct photolysis of cystine results mainly in S–S cleavage and with only minor degradation through C–S cleavage . Numerous products have been identified, such as cysteic acid formed from oxidation of Cys, which is formed by the reduction of cystine …”

Section: Introductionmentioning

confidence: 99%

“…12 In the presence of oxygen, degradation of cystine occurs only when the incident irradiation wavelength is below 300 nm in a reaction in which the quantum yield for the destruction of cystine is pHindependent. 13 Direct photolysis of cystine results mainly in S−S cleavage and with only minor degradation through C−S cleavage. 12 Numerous products have been identified, such as cysteic acid formed from oxidation of Cys, which is formed by the reduction of cystine.…”

Section: ■ Introductionmentioning

confidence: 99%

“…12 Numerous products have been identified, such as cysteic acid formed from oxidation of Cys, which is formed by the reduction of cystine. 13 Trp and Tyr may act as photosensitizers in proteins due to their UV-absorbing properties. The whey protein α-lactalbumin contains four Trp and four Tyr residues as well as four disulfide bonds, but no free cysteine (Cys) residues, which otherwise are required for heat-induced disulfide-mediated protein aggregation through thiol−disulfide exchange reactions.…”

Section: ■ Introductionmentioning

confidence: 99%

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Cleavage of Disulfide Bonds in Cystine by UV-B Illumination Mediated by Tryptophan or Tyrosine as Photosensitizers

Zhao

Poojary

Skibsted

et al. 2020

J. Agric. Food Chem.

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Photolytic cleavage of disulfide bonds in proteins by UV light will influence their structure and functionality. The present study aimed to investigate the efficiency of disulfide cleavage by UV-B light in a system without a protein backbone consisting of combinations of cystine (a disulfide) and tryptophan (Trp) or tyrosine (Tyr) under anaerobic and aerobic conditions and to identify oxidation products formed by UV-B light. Cystine was reduced to cysteine (Cys) almost with a 1:1 stoichiometry by photoexcited Trp for anaerobic equimolar aqueous solutions (each 200 μM; pH 7.0), while photoexcited Tyr provided lower concentrations of Cys. The calculation of apparent quantum yields allowed for a comparison between the efficiency of reactions and showed that formation of Cys from disulfide cleavage of cystine was more efficient by photoexcited Trp than by photoexcited Tyr and of cystine alone and that Trp was more sensitive to photodegradation than Tyr and cystine under both aerobic and anaerobic conditions. Increasing the ratio between cystine and Trp to a 1:2 ratio did not increase the efficiency of free thiol formation but caused a more efficient photodegradation of Trp. The free thiol formed from disulfide cleavage of cystine was further oxidized to other unidentified compounds. Trp oxidation products (3-hydroxykynurenine (3-OH-Kyn) and tryptamine) were only identified in minor concentrations following light exposure of cystine and Trp in 1:1 and 1:2 ratios under both aerobic and anaerobic conditions, indicating further photodegradation to unidentified compounds. 3,4-Dihydroxyphenylalanine (DOPA) was formed from the oxidation of Tyr in the illuminated samples of cystine and Tyr in a 1:1 ratio under both aerobic and anaerobic conditions.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Cleavage of Disulfide Bonds in Cystine by UV-B Illumination Mediated by Tryptophan or Tyrosine as Photosensitizers

Zhao

Poojary

Skibsted

et al. 2020

J. Agric. Food Chem.

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“…The formation of Ala during the photo-irradiation of cystine had been recognized several decades ago, but a satisfactory mechanism had not been postulated. 26–29 …”

Section: Introductionmentioning

confidence: 99%

Reversible Hydrogen Transfer Reactions of Cysteine Thiyl Radicals in Peptides: the Conversion of Cysteine into Dehydroalanine and Alanine, and of Alanine into Dehydroalanine

2011

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The photodissociation of disulfide bonds in model peptides containing Ala and Ala-d3 generates a series of photoproducts following the generation of a CysS• thiyl radical pair. These photoproducts include transformations of Cys to dehydroalanine (Dha) and Ala, as well as Ala to Dha. Intramolecular Michael addition of an intact Cys with a photolytically generated Dha results in the formation of cyclic thioethers. The conversion of Cys into Dha likely involves a 1,3-H-shift from the Cys αC-H bond to the thiyl radical, followed by elimination of HS•. The conversion of Dha into Ala most likely involves hydrated electrons, which are generated through the photolysis of Cys, the photoproduct of disulfide photolysis. Prior to stable product formation, CysS• radicals engage in reversible hydrogen transfer reactions with αC-H and βC-H bonds of the surrounding amino acids. Especially for the βC-H bonds of Ala such hydrogen transfer reactions are unexpected based on thermodynamic grounds; however, the replacement of deuterons in Ala-d3 by hydrogens in H2O provides strong experimental evidence for such reactions.

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Formation of the thioester, N,S-diacetylcysteine, from acetaldehyde and N,N′diacetylcystine in aqueous solution with ultraviolet light

Weber

1981

J Mol Evol

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The thioester, N,S-diacetylcysteine, is formed during the illumination of phosphate buffered (pH 7.0) aqueous solutions of acetaldehyde and N,N'-diacetylcystine with ultraviolet light. The yield of N,S-diacetylcysteine relative to N-acetylcysteine and unidentified products progressively increases as ultraviolet light below 239 nm, 253 nm and 281 nm is cut off with optical filters. When ultraviolet light below 320 nm is removed with an optical filter, there is no detectable reaction. Illumination of 0.025 M N,N'-diacetylcystine with 0.5 M and 1.0 M acetaldehyde with filtered ultraviolet light gives, respectively, 20% and 80% yields of N,S-diacetylcysteine. In the reaction with 1.0 M acetaldehyde, N-acetylcysteine forms early in the reaction and later decreases with its conversion to N,S-diacetylcysteine. The prebiotic significance of these reactions is discussed.

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The photochemical degradation of cystine in aqueous solutions in the presence of nitrogen

Cited by 10 publications

References 23 publications

Cleavage of Disulfide Bonds in Cystine by UV-B Illumination Mediated by Tryptophan or Tyrosine as Photosensitizers

Cleavage of Disulfide Bonds in Cystine by UV-B Illumination Mediated by Tryptophan or Tyrosine as Photosensitizers

Reversible Hydrogen Transfer Reactions of Cysteine Thiyl Radicals in Peptides: the Conversion of Cysteine into Dehydroalanine and Alanine, and of Alanine into Dehydroalanine

Formation of the thioester, N,S-diacetylcysteine, from acetaldehyde and N,N′diacetylcystine in aqueous solution with ultraviolet light

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