Mass Spectrometric Quantification of Markers for Protein Oxidation by Tyrosyl Radical, Copper, and Hydroxyl Radical in Low Density

Lipoprotein oxidation has been implicated in the pathogenesis of atherosclerosis. However, the physio-logically relevant pathways mediating oxidative dam-age have not yet been identified. Three potential mech-anisms are tyrosyl radical, hydroxyl radical, and redox active metal ions. Tyrosyl radical forms o,o*-dityrosine cross-links in proteins. The highly reactive hydroxyl radical oxidizes phenylalanine residues to o-tyrosine and m-tyrosine. Metal ions oxidize low density lipopro-tein (LDL) by poorly understood pathways. To explore the involvement of tyrosyl radical, hydroxyl radical, and metal ions in atherosclerosis, we developed a highly sensitive and quantitative method for measuring levels of o,o*-dityrosine, o-tyrosine, andm-tyrosine in proteins, lipoproteins, and tissue, using stable isotope dilutio