TY - JOUR
T1 - Singlet oxygen-mediated protein oxidation
T2 - evidence for the formation of reactive side chain peroxides on tyrosine residues
AU - Wright, Adam
AU - Bubb, William A
AU - Hawkins, Clare Louise
AU - Davies, Michael Jonathan
PY - 2002/7
Y1 - 2002/7
N2 - Singlet oxygen (1O2) is generated by a number of enzymes as well as by UV or visible light in the presence of a sensitizer and has been proposed as a damaging agent in a number of pathologies including cataract, sunburn, and skin cancers. Proteins, and Cys, Met, Trp, Tyr and His side chains in particular, are major targets for 1O2 as a result of their abundance and high rate constants for reaction. In this study it is shown that long-lived peroxides are formed on free Tyr, Tyr residues in peptides and proteins, and model compounds on exposure to 1O2 generated by both photochemical and chemical methods. The yield of these species is significantly enhanced in D2O and decreased by azide. Nuclear magnetic resonance and mass spectroscopic analysis of reaction mixtures, or materials separated by high-performance liquid chromatography, are consistent with the initial formation of an (undetected) endoperoxide that undergoes rapid ring-opening to give a hydroperoxide situated at the C1 ring-position (i.e. para to the phenolic group). In the presence of a free alpha-amino group (e.g. with free Tyr), rapid ring-closure occurs to give an indolic hydroperoxide that decays into the corresponding alcohol, 3a-hydroxy-6-oxo-2,3,3a,6,7,7a-hexahydro-1H-indole-2-carboxylic acid. Hydroperoxides that lack a free alpha-amino group (e.g. those formed on 3-(4-hydroxyphenyl)propionic acid, N-Ac-Tyr and Tyr-containing peptides) are longer-lived, with half-lives of hours to days. These species undergo slow decay at low temperatures to give the corresponding alcohol. Their rate of decay is enhanced at 37 degrees C, or on exposure to UV light or metal ions, and gives rise to reactive radicals, via cleavage of the peroxide bond. These radicals have been characterized by electron paramagnetic resonance spin trapping. These studies demonstrate that long-lived Tyr-derived peroxides are formed on proteins exposed to 1O2 and that these may promote damage to other targets via further radical generation.
AB - Singlet oxygen (1O2) is generated by a number of enzymes as well as by UV or visible light in the presence of a sensitizer and has been proposed as a damaging agent in a number of pathologies including cataract, sunburn, and skin cancers. Proteins, and Cys, Met, Trp, Tyr and His side chains in particular, are major targets for 1O2 as a result of their abundance and high rate constants for reaction. In this study it is shown that long-lived peroxides are formed on free Tyr, Tyr residues in peptides and proteins, and model compounds on exposure to 1O2 generated by both photochemical and chemical methods. The yield of these species is significantly enhanced in D2O and decreased by azide. Nuclear magnetic resonance and mass spectroscopic analysis of reaction mixtures, or materials separated by high-performance liquid chromatography, are consistent with the initial formation of an (undetected) endoperoxide that undergoes rapid ring-opening to give a hydroperoxide situated at the C1 ring-position (i.e. para to the phenolic group). In the presence of a free alpha-amino group (e.g. with free Tyr), rapid ring-closure occurs to give an indolic hydroperoxide that decays into the corresponding alcohol, 3a-hydroxy-6-oxo-2,3,3a,6,7,7a-hexahydro-1H-indole-2-carboxylic acid. Hydroperoxides that lack a free alpha-amino group (e.g. those formed on 3-(4-hydroxyphenyl)propionic acid, N-Ac-Tyr and Tyr-containing peptides) are longer-lived, with half-lives of hours to days. These species undergo slow decay at low temperatures to give the corresponding alcohol. Their rate of decay is enhanced at 37 degrees C, or on exposure to UV light or metal ions, and gives rise to reactive radicals, via cleavage of the peroxide bond. These radicals have been characterized by electron paramagnetic resonance spin trapping. These studies demonstrate that long-lived Tyr-derived peroxides are formed on proteins exposed to 1O2 and that these may promote damage to other targets via further radical generation.
KW - Animals
KW - Cattle
KW - In Vitro Techniques
KW - Oxidation-Reduction
KW - Peroxides
KW - Photochemistry
KW - Proteins
KW - Serum Albumin, Bovine
KW - Singlet Oxygen
KW - Tyrosine
M3 - Journal article
C2 - 12126305
SN - 0031-8655
VL - 76
SP - 35
EP - 46
JO - Photochemistry and Photobiology
JF - Photochemistry and Photobiology
IS - 1
ER -
