The determination of salivary biomarkers as a means of monitoring general health and for the early diagnosis of disease is of increasing interest in clinical research. Based on the linkage between salivary proteins and systemic diseases, the aim of this work was the identification of saliva proteins using proteomics. Salivary proteins were separated using two-dimensional (2-D) gel electrophoresis over a pH range between 3-10, digested, and then analyzed by matrix assisted laser desorption/ionization-time of flight (MALDI-TOF)-TOF mass spectrometry (MS) and tandem mass spectrometry (MS/MS). Proteins were identified using automated MS and MS/MS data acquisition. The resulting data were searched against a protein database using an internal Mascot search routine. Ninety spots give identifications with high statistical reliability. Of the identified proteins, 11 were separated and identified in saliva for the first time using proteomics tools. Moreover, three proteins that have not been previously identified in saliva, PLUNC, cystatin A, and cystatin B were identified.

In an effort to understand the mechanism of radical formation on heme proteins, the formation of radicals on hemoglobin was initiated by reaction with hydrogen peroxide in the presence of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The DMPO nitrone adducts were analyzed by mass spectrometry (MS) and immuno-spin trapping. The spin-trapped protein adducts were then subjected to tryptic digestion and MS analyses. When hemoglobin was reacted with hydrogen peroxide (H 2 O 2 ) in the presence of DMPO, a DMPO nitrone adduct could be detected by immuno-spin trapping. To verify that DMPO adducts of the protein free radicals had been formed, the reaction mixtures were analyzed by flow injection electrospray ionization mass spectrometry (ESI/MS). The ESI mass spectrum of the hemoglobin/H 2 O 2 /DMPO sample shows one adduct each on both the ␣ chain and the ␤ chain of hemoglobin which corresponds in mass to the addition of one DMPO molecule. The nature of the radicals formed on hemoglobin was explored using proteolysis techniques followed by liquid chromatography/mass spectrometry (LC/MS) and tandem mass spectrometry (MS/MS) analyses. The following sites of DMPO addition were identified on hemoglobin: Cys-93 of the ␤ chain, and Tyr-42, Tyr-24, and His-20 of the ␣ chain. Because of the pi-pi interaction of Tyr-24 and His-20, the unpaired electron is apparently delocalized on both the tyrosine and histidine residue (pi-pi stacked pair radical).

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