TY - JOUR

T1 - Riboflavin-induced Type 1 photo-oxidation of tryptophan using a high intensity 365 nm light emitting diode

AU - Silva, Eduardo

AU - Barrias, Pablo

AU - Fuentes-Lemus, Eduardo

AU - Tirapegui, Cristian

AU - Aspee, Alexis

AU - Carroll, Luke

AU - Davies, Michael J.

AU - Lopez-Alarcon, Camilo

PY - 2019

Y1 - 2019

N2 - The mechanism of photo-oxidation of tryptophan (Trp) sensitized by riboflavin (RF) was examined employinghigh concentrations of Trp and RF, with a high intensity 365 nm light emitting diode (LED) source under N2,20% and 100% O2atmospheres. Dimerization of Trp was a major pathway under the N2atmosphere, though thisoccurred with a low yield (DφTrp= 5.9 × 10−3), probably as a result of extensive back electron transfer re-actions between RF•-and Trp(H)•+. The presence of O2decreased the extent of this back electron transfer re-action, and the extent of Trp dimerization. This difference is attributed to the formation of O2•-(generated viaelectron transfer from RF•-to O2) which reacts rapidly with Trp•leading to extensive consumption of the parentamino acid and formation of peroxides and multiple other oxygenated products (N-formylkynurenine, alcohols,diols) of Trp, as detected by LC-MS. Thus, it appears that thefirst step of the Type 1 mechanism of Trp photo-oxidation, induced by this high intensity 365 nm light source, is an electron transfer reaction between the aminoacid and3RF, with the presence of O2modulating the subsequent reactions and the products formed, as a resultof O2•-formation. These data have potential biological significance as LED systems and RF-based treatments havebeen proposed for the treatment of pathological myopia and keratitis.

AB - The mechanism of photo-oxidation of tryptophan (Trp) sensitized by riboflavin (RF) was examined employinghigh concentrations of Trp and RF, with a high intensity 365 nm light emitting diode (LED) source under N2,20% and 100% O2atmospheres. Dimerization of Trp was a major pathway under the N2atmosphere, though thisoccurred with a low yield (DφTrp= 5.9 × 10−3), probably as a result of extensive back electron transfer re-actions between RF•-and Trp(H)•+. The presence of O2decreased the extent of this back electron transfer re-action, and the extent of Trp dimerization. This difference is attributed to the formation of O2•-(generated viaelectron transfer from RF•-to O2) which reacts rapidly with Trp•leading to extensive consumption of the parentamino acid and formation of peroxides and multiple other oxygenated products (N-formylkynurenine, alcohols,diols) of Trp, as detected by LC-MS. Thus, it appears that thefirst step of the Type 1 mechanism of Trp photo-oxidation, induced by this high intensity 365 nm light source, is an electron transfer reaction between the aminoacid and3RF, with the presence of O2modulating the subsequent reactions and the products formed, as a resultof O2•-formation. These data have potential biological significance as LED systems and RF-based treatments havebeen proposed for the treatment of pathological myopia and keratitis.

KW - LED

KW - Riboflavin

KW - Photobleaching

KW - Type 1/type 2 mechanisms

KW - Triplet excited state

KW - Tryptophan

KW - Photo-oxidation

KW - Dimers

KW - Trimers

KW - N-formylkynurenine

KW - Electron transfer

U2 - 10.1016/j.freeradbiomed.2018.11.026

DO - 10.1016/j.freeradbiomed.2018.11.026

M3 - Journal article

C2 - 30502456

VL - 131

SP - 133

EP - 143

JO - Free Radical Biology & Medicine

JF - Free Radical Biology & Medicine

SN - 0891-5849

ER -