TY - JOUR

T1 - Oxygenation is the main pathway for the reaction between superoxide anion and tryptophan radical

AU - Zhuravleva, Yuliya S.

AU - Sherin, Petr S.

PY - 2025/12/1

Y1 - 2025/12/1

N2 - Oxygenation, the covalent addition of oxygen, is the most common chemical modification of proteins, leading to the loss of their structure and functionality. Tryptophan (TrpH) within peptides and proteins is considered one of the main sources of electrons for cellular oxidants, and corresponding tryptophan radicals may have long lifetimes. The reaction between superoxide anion (O2•—) and tryptophan radicals (Trp•) is the fastest known bimolecular reaction of Trp•, which may lead to the irreversible oxygenation of TrpH. This reaction may proceed via the addition, yielding oxygenated forms of TrpH, or the electron transfer with the restoration of the initial reagents. Currently, the mechanism of this reaction remains unclear due to contradicting conclusions reported previously. This work aims to elucidate the mechanism of this reaction using methods of time-resolved optical spectroscopy to visualise processes on the microsecond time scale and liquid chromatography-mass spectrometry to analyse the reagent degradation and product accumulation. The target radicals were generated using natural photosensitiser kynurenic acid irradiated by pulsed laser radiation. Our time-resolved data demonstrated that TrpH undergoes rapid oxygenation under aerobic conditions without significant restoration of its ground state. Hydroxyperoxides and N-formyl-kynurenine were found to be major photoproducts of TrpH degradation. Altogether, our data unambiguously indicated the addition as the major pathway for the reaction between superoxide anion and tryptophan radicals. Comparison of experimentally measured yields of reagent degradation with those calculated from the kinetic scheme provided an opportunity to estimate the ratio between addition/electron transfer reactions as 7/1 for N-acetyl-L-tryptophan.

AB - Oxygenation, the covalent addition of oxygen, is the most common chemical modification of proteins, leading to the loss of their structure and functionality. Tryptophan (TrpH) within peptides and proteins is considered one of the main sources of electrons for cellular oxidants, and corresponding tryptophan radicals may have long lifetimes. The reaction between superoxide anion (O2•—) and tryptophan radicals (Trp•) is the fastest known bimolecular reaction of Trp•, which may lead to the irreversible oxygenation of TrpH. This reaction may proceed via the addition, yielding oxygenated forms of TrpH, or the electron transfer with the restoration of the initial reagents. Currently, the mechanism of this reaction remains unclear due to contradicting conclusions reported previously. This work aims to elucidate the mechanism of this reaction using methods of time-resolved optical spectroscopy to visualise processes on the microsecond time scale and liquid chromatography-mass spectrometry to analyse the reagent degradation and product accumulation. The target radicals were generated using natural photosensitiser kynurenic acid irradiated by pulsed laser radiation. Our time-resolved data demonstrated that TrpH undergoes rapid oxygenation under aerobic conditions without significant restoration of its ground state. Hydroxyperoxides and N-formyl-kynurenine were found to be major photoproducts of TrpH degradation. Altogether, our data unambiguously indicated the addition as the major pathway for the reaction between superoxide anion and tryptophan radicals. Comparison of experimentally measured yields of reagent degradation with those calculated from the kinetic scheme provided an opportunity to estimate the ratio between addition/electron transfer reactions as 7/1 for N-acetyl-L-tryptophan.

KW - Superoxide anion

KW - Tryptophan radical

KW - UV-A light

KW - Kynurenic acid

KW - Oxygenation

KW - Tryptophan hydroperoxides and peroxides

UR - https://www.mendeley.com/catalogue/d043dffb-6f3b-3a49-b4a4-f2fd448317b9/

UR - https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=105009431521&origin=inward

U2 - 10.1016/j.jphotochem.2025.116571

DO - 10.1016/j.jphotochem.2025.116571

M3 - Article

SP - 116571

JO - Journal of Photochemistry and Photobiology A: Chemistry

JF - Journal of Photochemistry and Photobiology A: Chemistry

SN - 1010-6030

ER -