Sensitizer-mediated photooxidation of histidine residues: evidence for the formation of reactive side-chain peroxides

TY - JOUR

T1 - Sensitizer-mediated photooxidation of histidine residues

T2 - evidence for the formation of reactive side-chain peroxides

AU - Agon, Vanessa V

AU - Bubb, William A

AU - Wright, Adam

AU - Hawkins, Clare Louise

AU - Davies, Michael Jonathan

PY - 2006/2/15

Y1 - 2006/2/15

N2 - Exposure of proteins to visible light in the presence of a sensitizer results in the oxidation of Met, Trp, Tyr, Cys, and His side chains. These reactions are only partially understood, particularly with His. In this study, the oxidation of free His, His derivatives, and His-containing peptides has been examined using visible light and a range of sensitizers. It is shown that photooxidation gives rise to unstable peroxides, in a light-, illumination time-, and sensitizer-dependent manner. The yield of these materials is increased when reactions are carried out in solutions prepared with D2O, which prolongs the lifetime of 1O2, and decreased in the presence of the potent 1O2 scavenger azide, consistent with the involvement of this excited state. These peroxides have half-lives of hours, though the rate of decomposition is enhanced by elevated temperatures, reductants, and metal ions. Reducing metal ions catalyze the formation of radicals, which have been detected by EPR spin trapping. Structural analysis of His photo-products using NMR spectroscopy has provided evidence for the formation of oxygenated and cyclized compounds (e.g., 6a-hydroxy-2-oxo-octahydro-pyrollo[2,3-d]imidazole-5-carboxylic acid) and cross-linked materials. The latter materials may be partly responsible for the high yield of aggregated materials detected on photooxidation of His-containing proteins.

AB - Exposure of proteins to visible light in the presence of a sensitizer results in the oxidation of Met, Trp, Tyr, Cys, and His side chains. These reactions are only partially understood, particularly with His. In this study, the oxidation of free His, His derivatives, and His-containing peptides has been examined using visible light and a range of sensitizers. It is shown that photooxidation gives rise to unstable peroxides, in a light-, illumination time-, and sensitizer-dependent manner. The yield of these materials is increased when reactions are carried out in solutions prepared with D2O, which prolongs the lifetime of 1O2, and decreased in the presence of the potent 1O2 scavenger azide, consistent with the involvement of this excited state. These peroxides have half-lives of hours, though the rate of decomposition is enhanced by elevated temperatures, reductants, and metal ions. Reducing metal ions catalyze the formation of radicals, which have been detected by EPR spin trapping. Structural analysis of His photo-products using NMR spectroscopy has provided evidence for the formation of oxygenated and cyclized compounds (e.g., 6a-hydroxy-2-oxo-octahydro-pyrollo[2,3-d]imidazole-5-carboxylic acid) and cross-linked materials. The latter materials may be partly responsible for the high yield of aggregated materials detected on photooxidation of His-containing proteins.

KW - Histidine

KW - Light

KW - Magnetic Resonance Spectroscopy

KW - Oxidation-Reduction

KW - Peptide Fragments

KW - Peroxides

KW - Photochemistry

KW - Singlet Oxygen

U2 - 10.1016/j.freeradbiomed.2005.09.039

DO - 10.1016/j.freeradbiomed.2005.09.039

M3 - Journal article

C2 - 16458201

SN - 0891-5849

VL - 40

SP - 698

EP - 710

JO - Free Radical Biology & Medicine

JF - Free Radical Biology & Medicine

IS - 4

ER -