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PubMed2004

Bicarbonate enhances alpha-synuclein oligomerization and nitration: intermediacy of carbonate radical anion and nitrogen dioxide radical.

alpha-Synuclein, a neuronal presynaptic protein, has been reported to undergo oligomerization to form toxic Lewy bodies in neurodegenerative disorders. One of the proposed mechanisms for aggregation of alpha-synuclein involves oxidative and nitrative modifications. In the present study, we show that addition of 3-morpholino-sydnonimine chloride (SIN-1) or slow infusion of pre-formed peroxynitrite (ONOO-) to mixtures containing alpha-synuclein and HCO3- markedly enhanced both nitration and aggregation of alpha-synuclein through dityrosine formation. Bicarbonate-dependent peroxidase activity of Cu,Zn-superoxide dismutase (SOD1) also induced covalent aggregation of alpha-synuclein via a CO3*--dependent mechanism. Nitrone spin traps completely inhibited CO3*--mediated oxidation/nitration and aggregation of alpha-synuclein. Conversely, alpha-synuclein inhibited CO3*--induced spin adduct formation. Independent evidence for CO3*--mediated oxidation and dimerization of alpha-synuclein was obtained from UV photolysis of [(NH3)5CoCO3]+, which generates authentic CO3*-. Irradiation of [(NH3)5CoCO3]+ and NO2- in the presence of alpha-synuclein yielded nitration and aggregation products that were similar to those obtained from a SIN-1 (or slowly infused ONOO-) and HCO3- or a myeloperoxidase/H2O2/NO2- system. Hydrophobic membranes greatly influenced alpha-synuclein aggregation and nitration in these systems. We conclude that both CO3*- and NO2* could play a major role in the nitration/aggregation of alpha-synuclein.

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PubMed1986

Effects of nitrogen dioxide and nitrate nutrition on nodulation, nitrogenase activity, growth, and nitrogen content of bean.

The influence of nutrient nitrate level (0-20 millimolar) on the effects of NO(2) (0-0.5 parts per million) on nodulation and in vivo acetylene reduction activity of the roots and on growth and nitrate and Kjeldahl N concentration in shoots was studied in bean (Phaseolus vulgaris L. cv Kinghorn Wax) plants. Exposing 8-day old seedlings for 6 hours each day, for 15 days, to 0.02 to 0.5 parts per million NO(2) decreased total nodule weight at 0 and 1 millimolar nitrate, and nitrogenase (acetylene reduction) activity at all concentrations of nitrate. The pollutant had little effect on root fresh or dry weights. Shoot growth was inhibited by NO(2). The NO(2) exposure increased nitrate concentration in roots only at 20 millimolar nutrient nitrate. Exposure to NO(2) markedly increased Kjeldahl N concentration in roots but generally decreased that in shoots. The experiments demonstrated that nutrient N level and NO(2) concentration act jointly in affecting nodulation and N fixing capability, plant growth and composition, and root/shoot relationships of bean plants.

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PubMed2002

Direct real-time evaluation of nitration with green fluorescent protein in solution and within human cells reveals the impact of nitrogen dioxide vs. peroxynitrite mechanisms.

3-Nitrotyrosyl adducts in proteins have been detected in a wide range of diseases. The mechanisms by which reactive nitrogen oxide species may impede protein function through nitration were examined by using a unique model system, which exploits a critical tyrosyl residue in the fluorophoric pocket of recombinant green fluorescent protein (GFP). Exposure of purified GFP suspended in phosphate buffer to synthetic peroxynitrite in either 0.5 or 5 microM steps resulted in progressively increased 3-nitrotyrosyl immunoreactivity concomitant with disappearance of intrinsic fluorescence (IC(50) approximately 20 microM). Fluorescence from an equivalent amount of GFP expressed within intact MCF-7 tumor cells was largely resistant to this bolus treatment (IC(50) > 250 microM). The more physiologically relevant conditions of either peroxynitrite infusion (1 microM/min) or de novo formation by simultaneous, equimolar generation of nitric oxide (NO) and superoxide (e.g., 3-morpholinosydnonimine; NONOates plus xanthine oxidase/hypoxanthine, menadione, or mitomycin C) were examined. Despite robust oxidation of dihydrorhodamine under each of these conditions, fluorescence decrease of both purified and intracellular GFP was not evident regardless of carbon dioxide presence, suggesting that oxidation and nitration are not necessarily coupled. Alternatively, both extra- and intracellular GFP fluorescence was exquisitely sensitive to nitration produced by heme-peroxidase/hydrogen peroxide-catalyzed oxidation of nitrite. Formation of nitrogen dioxide (NO(2)) during the reaction between NO and the nitroxide 2-phenyl-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide indicated that NO(2) can enter cells and alter peptide function through tyrosyl nitration. Taken together, these findings exemplified that heme-peroxidase-catalyzed formation of NO(2) may play a pivotal role in inflammatory and chronic disease settings while calling into question the significance of nitration by peroxynitrite.

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