Reactive Nitrogen Oxide Species-Induced Post-Translational Modifications in Human Hemoglobin and the Association with Cigarette Smoking

Nitric oxide (NO) is essential for normal physiology, but excessive production of NO during inflammatory processes can damage the neighboring tissues. Reactive nitrogen oxide species (RNOx), including peroxynitrite (ONOO-), are powerful nitrating agents. Biological protein nitration is involved in several disease states, including inflammatory diseases, and it is evident by detection of 3-nitrotyrosine (3NT) in inflamed tissues. In this study, we identified peroxynitrite-induced post-translational modifications (PTMs) in human hemoglobin by accurate mass measurement as well as by the MS2 and MS3 spectra. Nitration on Tyr-24, Tyr-42 (alpha-globin), and Tyr-130 (beta-globin) as well as nitrosation on Tyr-24 (alpha-globin) were identified. Also characterized were oxidation of all three methionine residues, alpha-Met-32, alpha-Met-76, and beta-Met-SS to the sulfoxide, as well as cysteine oxidation determined as sulfinic acid on alpha-Cys-104 and sulfonic acid on alpha-Cys-104, beta-Cys-93, and beta-Cys-112. These modifications are detected in hemoglobin freshly isolated from human blood and the extents of modifications were semiquantified relative to the reference peptides by nanoflow liquid chromatography-nanospray ionization tandem mass spectrometry (nanoLC-NSI/MS/MS) under the selected reaction monitoring (SRM) mode. The results showed a statistically significant positive correlation between cigarette smoking and the extents of tyrosine nitration at alpha-Tyr-24 and at alpha-Tyr-42. To our knowledge, this is the first report on identification and quantification of multiple PTMs in hemoglobin from human blood and association of a specific 3NT-containing peptide with cigarette smoking. This highly sensitive and specific assay only requires hemoglobin isolated from one drop (similar to 10 mu L) of blood. Thus, measurement of these PTMs in hemoglobin might be feasible for assessing nitrative stress in vivo.