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l ‐Tryptophan Interactions with the Horseradish Peroxidase‐Catalyzed Generation of Triplet Acetone
Author(s) -
Ramos Luiz D.,
Prado Fernanda M.,
Stevani Cassius V.,
Di Mascio Paolo,
Bechara Etelvino J. H.
Publication year - 2021
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.13363
Subject(s) - chemistry , horseradish peroxidase , photochemistry , adduct , quenching (fluorescence) , acetone , radical , hydrogen atom abstraction , tryptophan , singlet state , phosphorescence , triplet state , excited state , molecule , enzyme , organic chemistry , amino acid , fluorescence , biochemistry , physics , quantum mechanics , nuclear physics
Abstract Triplet carbonyls generated by chemiexcitation are involved in typical photobiochemical processes in the absence of light. Due to their biradical nature, ultraweak light emission and long lifetime, electronically excited triplet species display typical radical reactions such as isomerization, fragmentation, cycloaddition and hydrogen abstraction. In this paper, we report chemical reactions in a set of amino acid residues induced by the isobutanal/horseradish peroxidase (IBAL/HRP) system, a well‐known source of excited triplet acetone (Ac 3* ). Accordingly, quenching of Ac 3* by tryptophan (Trp) unveiled parallel enzyme damage and inactivation, likely explained by scavenging of IBAL tertiary radical reaction intermediate and Ac 3* ‐derived 2‐hydroxy‐ i ‐propyl radical. Quenching constants were calculated from Stern–Volmer plots, and the structure of radical adducts was revealed by mass spectrometry. As expected, a concurrent Schiff‐type adduct was found to be one of the reaction by‐products. These findings draw attention to potential structural and functional changes in enzymes involved in the electronic chemiexcitation of their products.