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 - 2019/2/1
Y1 - 2019/2/1
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
SN - 0891-5849
VL - 131
SP - 133
EP - 143
JO - Free Radical Biology and Medicine
JF - Free Radical Biology and Medicine
ER -