Photo-oxidation of lysozyme triggered by riboflavin is O2-dependent, occurs via mixed type 1 and type 2 pathways, and results in inactivation, site-specific damage and intra- and inter-molecular crosslinks

Photosensitization Reactions of Biomolecules: Definition, Targets and Mechanisms

“…In particular, • S-OH may further react with O 2 by either addition or by one-electron oxidation (reaction 15), whereas S(-H) In some cases, O 2 is needed in the overall process to avoid the recovery of the substrate via reaction 11, that is, O 2 , by quenching Sens •-(reaction 6), prevents the recombination of radicals and favors the reaction between two S(-H) • (30). In other cases, O 2 is not needed at all and S 2 can be formed under anaerobic conditions, even with higher efficiencies than in the presence of O 2 (31). Whether O 2 favors or hinders the photosensitized formation of S 2 through these mechanisms depend on many factors.…”

Formation and characterization of crosslinks, including Tyr–Trp species, on one electron oxidation of free Tyr and Trp residues by carbonate radical anion

“…This tenet is supported by the detection of both intra-and intermolecular Tyr-Trp bonds in a number of systems. 36,37,[48][49][50]57 In spite of this, little effort has been expended on understanding the factors that control the formation, accumulation and biological consequences of the generation of this type of species. This is probably, at least in part, due to the absence of robust methods to detect and quantify these adducts.…”

“…Dimerization of Trp residues and consequent protein crosslinking has been less well studied than with di-Tyr, though a number of examples have been reported in the literature. 31,36,37,40 Pulse radiolysis studies indicate that dimerization of Trp occurs with k $1 Â 10 8 M À1 s À1 for both free and peptide Trp residues. 28 Exposure of Trp-containing peptides and lysozyme to Co 60 g-radiation, peroxynitrous acid (ONOOH), or CO 3 À derived from the bovine SOD1/hydrogen peroxide system, has been reported to yield at least four ditryptophan isomers (detected as ions with m/z 407 by MS), and with different retention times; this consistent with the delocalization of the unpaired electron across the indole ring of Trp with signicant spin density present at N1 and C3 of the pyrrole ring, as well as carbon atoms of the benzene ring.…”

“…[32][33][34] Ditryptophan bonds have also been detected in crosslinked lysozyme, caseins, crystallin proteins, and mixed lysozyme-hSOD1 species, as a result of protein modication by multiple oxidants and photochemical reactions. [35][36][37][38][39][40] Despite the increasing number of reports on ditryptophan formation, the signicance of this species in human disease, and the factors that modulate its formation are not fully understood. Recent data indicate that ditryptophan yields are diminished under aerobic conditions due to the occurrence of competing reactions involving O 2 , and that multiple ditryptophan isomers, including both C-C and C-N linked species can be formed.…”

“…Tyr-Trp crosslinks have been reported in a cytochrome c peroxidase mutant, with these generated via a peroxide-dependent process, 48 in the vicinity of the active site of a catalaseperoxidase from Haloarcula marismortui, 49 and in oxidized samples of lysozyme and glucose 6-phosphate dehydrogenase. 36,37,50 Studies on these species have however been limited by a lack of information on the structure of these species, methods that allow their detection and characterization, and authentic standards that would facilitate their quantication.…”