Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.6.3.1 (NADPH oxidase)
 11,281 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To kill invading bacteria, viruses, and fungi, phagocytes secrete hydrogen peroxide (H(2)O(2)) and the heme enzyme myeloperoxidase. We have explored the possibility that myeloperoxidase might use H(2)O(2) to convert L-tyrosine to tyrosyl radical. Activated human neutrophils and monocytes used the system to oxidize free L-tyrosine to o,o'-dityrosine, a stable product of tyrosyl radical. Protein-bound tyrosyl residues exposed to myeloperoxidase, H(2)O(2), and L-tyrosine were also oxidized to o,o'-dityrosine. The cross-linking reaction required free L-tyrosine, suggesting that myeloperoxidase converts the amino acid to a diffusible radical catalyst that promotes protein oxidation. We used electron paramagnetic resonance to provide direct evidence that the oxidizing intermediate is free tyrosyl radical. Myeloperoxidase-generated tyrosyl radical also initiates lipid peroxidation, suggesting that activated phagocytes might also be able to oxidize lipids in host tissues. Moreover, myeloperoxidase is present and active in human atherosclerotic tissue, and levels of protein-bound dityrosine are elevated in such lesions. Our recent studies indicate that activated neutrophils use oxidants generated by the phagocyte NADPH oxidase to produce protein-bound dityrosine during acute inflammation. Collectively, these findings suggest that generation of tyrosyl radical by myeloperoxidase allows activated phagocytes to damage both proteins and lipids. Elevated levels of o,o'-dityrosine have been detected in inflammatory lung disease, neurodegenerative disorders, and aging. Thus, oxidation of tyrosine to tyrosyl radical might play a role in the pathogenesis of many diseases.
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PMID:Tyrosyl radical production by myeloperoxidase: a phagocyte pathway for lipid peroxidation and dityrosine cross-linking of proteins. 1212 92

3-nitro-L-tyrosine is formed by nitric oxide following different pathways such as NADPH oxidase, xanthine oxidase or glutamate NMDA receptor activation and is involved in the pathology of different neurological disorders. Unlike estradiol, a neuroprotective role of androgens against oxidative cell injury has not been fully investigated. This work targets the possible effects of testosterone on neuroblastoma cells exposed to 3-nitro-L-tyrosine. C1300 mouse undifferentiated neuroblastoma cells exposed to 3-nitro-L-tyrosine were cultured in the presence of testosterone. Morphological examination, proliferation and nuclear viability assays were performed. The expression of tyrosinated alpha-tubulin and incorporation of 3-nitro-L-tyrosine into protein were also estimated. Cells exposed to 3-nitro-L-tyrosine showed globular shape, reduced cytoplasmic processes and growth inhibition in comparison with controls. When testosterone was added to the medium, these changes were not evident. In addition, testosterone induced an upregulation of tyrosinated alpha-tubulin, a marker of neuronal plasticity, and a decrease in 3-nitro-L-tyrosine incorporation into tubulin. Our results suggest that testosterone exposure can diminish 3-nitro-L-tyrosine toxic effects on the morphology and growth rate of neuroblastoma cells. The upregulation of tyrosinated alpha-tubulin in testosterone-exposed cells would be consistent with concurrent plasticity events. Failure in alpha-tubulin nitration detected in cells exposed to both 3-nitro-L-tyrosine and testosterone, may support the idea that testosterone interferes with 3-nitro-L-tyrosine protein incorporation. Moreover, testosterone-induced neuroprotection likely entails a linkage with the androgen receptor as is suggested by the flutamide-induced inhibition of the hormone activity. Finally, the neuroprotective effects of testosterone in neuroblastoma cells could deal with the cellular antioxidant defence system, as shown by testosterone-induced increase in catalase activity.
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PMID:Testosterone induces neuroprotection from oxidative stress. Effects on catalase activity and 3-nitro-L-tyrosine incorporation into alpha-tubulin in a mouse neuroblastoma cell line. 1664 86