Singlet Molecular Oxygen Generation in the Reaction of Biological Haloamines of Amino Acids and Polyamines with Hydrogen Peroxide†.

Leucocytes generate hypohalous acids (HOCl and HOBr) to defend the host against pathogens. In cells, hypohalous acids react with amine-containing molecules, such as amino acids and polyamines, producing chloramines and bromamines, reservoirs of oxidizing power that can potentially damage host tissues at sites of inflammation. Hypohalous acids also react with H2 O2 to produce stoichiometric amounts of singlet molecular oxygen ( 1 O 2 ), but its generation in leucocytes is still under debate. Additionally, it is unclear whether haloamines generate 1 O 2 following a reaction with H2 O2 . Herein, we provide evidence of the generation of 1 O 2 in the reactions between amino acid-derived (taurine, N-α-acetyl-Lysine and glycine) and polyamine-derived (spermine and spermidine) haloamines and H2 O2 in an aqueous solution. The unequivocal formation of 1 O 2 was detected by monitoring its characteristic monomol light emission at 1270 nm in the near-infrared region. For amino acid-derived haloamines, the presence of 1 O 2 was further confirmed by chemical trapping with anthracene-9,10-divinylsulfonate and HPLC-MS/MS detection. Altogether, photoemission and chemical trapping studies demonstrated that chloramines were less effective at producing 1 O 2 than bromamines of amino acids and polyamines. Thus, 1 O 2 formation via bromamines and H2 O2 may be a potential source of 1 O 2 in nonilluminated biological systems.

Dehydromethionine is a common product of methionine oxidation by singlet molecular oxygen and hypohalous acids.

Methionine is one of the main targets for biological oxidants. Its reaction with the majority of oxidants generates only methionine sulfoxide. However, when N-terminal methionine reacts with hypohalous acids (HOCl and HOBr) or singlet molecular oxygen (1O2), it can also generate a cyclic product called dehydromethionine (DHM). Previously, DHM was suggested as a biomarker of oxidative stress induced by hypohalous acids. However, DHM can also be generated by 1O2 -oxidation of methionine, and the contribution of this pathway of DHM formation in a context of a site-specific redox imbalance in an organism is unknown. In this work, a through comparison of the reactions of hypohalous acids and 1O2 with methionine, either free or inserted in peptides and proteins was undertaken. In addition, we performed methionine photooxidation in heavy water (H218O) to determine the influence of the pH in the mechanism of DHM formation. We showed that for free methionine, or methionine-containing peptides, the yields of DHM formation in the reactions with 1O2 were close to those achieved by HOBr oxidation, but much higher than the yields obtained with HOCl as the oxidant. This was true for all pH tested (5, 7.4, and 9). Interestingly, for the protein ubiquitin, DHM yields after reaction with 1O2 were higher than those obtained with both hypohalous acids. Our results indicate that 1O2 may also be an important source of DHM in biological systems.