Reactions of superoxide with the myoglobin tyrosyl radical

Conjugation of Glutathione to Oxidized Tyrosine Residues in Peptides and Proteins

“…The synthetic peptide ELGYQG, an analog of the tryptic peptide 148 -153 that contains Tyr-151, was initially examined. As observed previously (16), treatment with the HRP/XO system produced a hydroperoxide (not shown), which decomposed at 37°C overnight and gave rise to peaks of m/z 682.3 corresponding to the hydroxide (Fig. 4a).…”

“…The reaction was stopped by adding catalase (10 -20 g/ml), decreasing the volume to half using a vacuum concentrator, then removing the enzymes using a 10-or 50-kDa cut off Amicon Ultra Free-MC Biomax Polysulfone filter (Millipore, Bedford, MA). For ELGYQG, a similar protocol was used except that XO (typically 0.0006 units/ml; superoxide generation 1.5 M/min) was added to a solution containing 0.2 mM peptide, 2.5 mM acetaldehyde, and 140 nM HRP (16). Reactions were run for 30 min at 22°C.…”

“…Sperm whale myoglobin was chosen because it reacts with H 2 O 2 to form a radical on Tyr-151 (19), and this radical can combine with superoxide to form an addition product (16). The synthetic peptide ELGYQG, an analog of the tryptic peptide 148 -153 that contains Tyr-151, was initially examined.…”

“…This would result in a conjugate with GSH (Scheme 1, reaction 4), and the reaction is a potential mechanism for cross-linking between Tyr and Cys residues in proteins. We have investigated whether this is the case for glutathionylation using small Tyr-containing peptides as well as sperm whale myoglobin, which we have previously shown to form a tyrosyl hydroperoxide derivative when treated with superoxide and hydrogen peroxide (16). We show that GSH reduces the peptide hydroperoxide to hydroxide derivatives (Tyr hydroxide), which readily and efficiently form conjugates.…”

Photodynamic Therapy: Current Status and Future Directions

“…As mentioned earlier, the tyrosyl radical reacts with O 2 - ∙ at an almost diffusion-limited rate [33]. Such reaction leads to either regeneration of tyrosine or the addition of O 2 - ∙ to form tyrosine hydroperoxide [58,59]. In proteins, the formation of tyrosine hydroperoxide is favored when the tyrosine is at the N-terminus [58].…”