Tyrosine, with peroxidizing lipid

Nitric oxide released by macrophages during inflammation reacts with active oxygen to form peroxynitrite. Peroxynitrite nitrates protein and peroxidizes lipids. y-Tocopherol (the principal form of vitamin E in the United States diet) and a-tocopherol (the major form present in the European diet and in supplements), both protect against peroxynitrite-induced lipid oxidation. [13]. Christen et al. reported that lipid hydroperoxide formation in liposomes is inhibited more effectively by y-tocopherol than a-tocopherol by a non-antioxidant mechanism [14]. However, Goss et al. [15] concluded that the presence of a-tocopherol attenuates nitration of both y-tocopherol and tyrosine, showing that nitration of... 

It follows from the above that MPO may catalyze the formation of chlorinated products in media containing chloride ions. Recently, Hazen et al. [172] have shown that the same enzyme catalyzes lipid peroxidation and protein nitration in media containing physiologically relevant levels of nitrite ions. It was found that the interaction of activated monocytes with LDL in the presence of nitrite ions resulted in the nitration of apolipoprotein B-100 tyrosine residues and the generation of lipid peroxidation products 9-hydroxy-10,12-octadecadienoate and 9-hydroxy-10,12-octadecadienoic acid. In this case there might be two mechanisms of MPO catalytic activity. At low rates of nitric oxide flux, the process was inhibited by catalase and MPO inhibitors but not SOD, suggesting the MPO initiation. 

Methyl - 4 - phenyl -1,2,3,6 - tetrahydropyridine (MPTP) is a frequently used animal model for Parkinson s disease. When injected into animals, MPTP is taken up by the cells in the substantia nigra where monoamino oxidase B (EC 1.4.3.4) converts it to l-methyl-4-phenylpyridinium ion (MPP ). This ion induces free radicals and duplicates many of the signs of Parkinson s disease in animals. In mice melatonin attenuated the resulting damage in the central nervous system (Acuna-Castroviejo et al. 1997). MPTP-induced neural lipid peroxidation was reduced to control levels when melatonin was co-administered with the herbicide. Neuronal loss and MPTP-induced reduction of tyrosine hydroxylase (EC 1.14.16.2) activity in neurones of the striatum were attenuated by melatonin. 

Coinfusion of iron and melatonin, 60 [tg/pl, but not 20 ng/jtl, prevented iron-induced elevation of lipid peroxidation in substantia nigra and iron-induced depletion of dopamine in rat striatum (Lin and Ho 2000). Intranigral infusion of melatonin (60 ng/pl) or etbanol (20 %) alone altered neither basd lipid peroxidation in substantia nigra or dopamine content in tbe ipsilateral striatum. Coinfusion of melatonin (60 [xg/pl) prevented the iron-induced reduction in tyrosine hydroxylase immunoreactive fibres in the striatum ipsilateral to iron-infused substantia nigra compared with that of the intact side. By contrast, the density of tyrosine hydroxylase positive axons in the melatonin + iron group was similar to that of the intact side of the same rat. 

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