Dityrosine, a specific marker of oxidation, is synthesized by the myeloperoxidase-hydrogen peroxide system of human neutrophils and macrophages.
Myeloperoxidase, secreted by activated phagocytes, produces the powerful cytotoxin hypochlorous acid from H2O2 and Cl-. We show that the enzyme can also employ H2O2 to oxidize L-tyrosine to tyrosyl radical, yielding the stable cross-linked product dityrosine. Dityrosine synthesis by the myeloperoxidase-H2O2 system did not require halide and was partially inhibited by Cl-. At physiological concentrations of Cl-, L-tyrosine, and other plasma amino acids, purified myeloperoxidase utilized 26% of the H2O2 in the reaction mixture to form dityrosine. Aminotriazole, cyanide, and azide inhibited the reaction. Phorbol ester-stimulated human neutrophils and monocyte-derived macrophages similarly generated dityrosine from L-tyrosine by a pathway inhibited by catalase, aminotriazole, and azide. The requirement for H2O2 and the inhibition by heme poisons suggest that activated phagocytes synthesize dityrosine by a peroxidative mechanism. These results indicate that L-tyrosine can compete effectively with Cl- as a substrate for myeloperoxidase and raise the possibility that formation of tyrosyl radical may play a role in the phagocyte inflammatory response. Because dityrosine is protease-resistant, stable to acid hydrolysis, and intensely fluorescent, its identification in tissues may pinpoint targets where phagocytes inflict oxidative damage in vivo.
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
J W
JW
Heinecke
W
W
Li
H L
HL
Daehnke
J A
JA
Goldstein
D002478:Cells, Cultured; D002853:Chromatography, Liquid; D005609:Free Radicals; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008264:Macrophages / Q000201:enzymology / Q000378:metabolism*; D013058:Mass Spectrometry; D009504:Neutrophils / Q000201:enzymology / Q000378:metabolism*; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000378:metabolism*; D013057:Spectrum Analysis; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000378:metabolism
D005609:Free Radicals; D014443:Tyrosine; D006861:Hydrogen Peroxide; C007543:dityrosine; D009195:Peroxidase