Sensitized photooxidation of histidine and its derivatives. Products and mechanism of the reaction

Abstract

In connection with the chemical modification of protein, the photooxidation of histidine and N-benzoylhistidine was investigated. It was confirmed that histidine is photooxidized to aspartic acid and urea via several intermediate compounds. The isolation of the intermediates as pure compounds, however, was difficult because of their instability during the purification. In the photooxidation of N-benzoylhistidine also, besides the final products, many kinds of intermediate products were detected and among them 17 compounds were isolated in pure state and characterized. The structures of five compounds were determined, and those of other five compounds were proposed. The same products were obtained when riboflavin or rose bengal instead of methylene blue was used as the photosensitizer in the photooxidation of N-benzoylhistidine though their relative

Oxidative modification of cytochrome c by singlet oxygen

“…Ozonolysis of His results initially in a +48 adduct identified by MS 2 as 2-amino-4-oxo-4-(3-formylureido)butanoic acid followed by decomposition to asparagine, the -22 adduct [55,56]. This conversion is also consistent with the earliest reports of His photooxidation [14], but does not represent the major product detected following minimal reaction with 1 O 2 with the products detected by MS. With its relative intensity and unique mass increment, the peptides derived from Cyt-c containing a His33 +14 modification have the potential to be used as a marker for the presence of mitochondrial 1 O 2 .…”

“…The LC-MS 2 spectrum of the peptide identified as the -22 adduct is shown in Figure 7A. This spectrum confirms the sequence of the peptide and is consistent with a multiple oxidation of the His residue to asparagine [14]. Ozonolysis of His results initially in a +48 adduct identified by MS 2 as 2-amino-4-oxo-4-(3-formylureido)butanoic acid followed by decomposition to asparagine, the -22 adduct [55,56].…”

“…Among the proteogenic amino acids, His, Tyr, Met, Cys, and Trp are known to undergo rapid chemical reaction with 1 O 2 at physiological pH [12,13]. Model reactions of singlet oxygen with His [14][15][16] and Trp [17] have resulted in the identification of numerous different products, but the major reaction pathways are summarized in Figure 1. While numerous studies have shown 1 O 2 can inactivate enzymes [13,18], classical studies identified the modified residue types by losses detected following acid hydrolysis and amino acid analysis [13] [19].…”

“…We attribute these observations to the potential for His26 oxidized to the 2-imidazolone to form a crosslink by addition of the ε amine of Lys27 to the electrophilic imine-one. Previous studies of His or imidazole oxidation have provided significant precedents for this addition [14] [57] [15]. This intramolecular crosslink would prevent the tryptic digestion following Lys27, and eliminate the potential to observe MS 2 peaks corresponding to cleavage of the His26-Lys27 peptide bond.…”

Singlet Oxygen Produced by Photodynamic Action Causes Inactivation of the Mitochondrial Permeability Transition Pore

“…Free histidine residues can be photodegraded to several different compounds after cycloaddition of 1 O 2 (29). Based on the inactivating effects of irradiation on the pore, one can speculate that histidine degradation following cleavage of the imidazole ring by 1 O 2 may suppress the regulation of pore opening which depends on histidine protonation-deprotonation.…”