Amino acids reactions with superoxide

In earlier studies [5,6] superoxide detection in mitochondria was equated to hydrogen peroxide formation. However, while it is quite possible that superoxide is a stoichiometric precursor of mitochondrial hydrogen peroxide, it is understandable that the level of hydrogen peroxide may be decreased due to the reactions with various mitochondrial oxidants. Moreover, superoxide level can be underestimated due to the reaction with mitochondrial MnSOD. Several authors [7,8] assumed that mitochondrial superoxide production may be estimated through cyanide-resistant respiration, which supposedly characterizes univalent dioxygen reduction. This method was applied for the measurement of superoxide production under in vitro normoxic and hyperoxic conditions, in spite of the finding [7] that cyanide-resistant respiration reflects also the oxidation of various substrates (lipids, amino acids, and nucleotides). Earlier,... 

Reaction of trans-peroxynitrite with superoxide dismutase. The placement of positively charged amino acids around the active site facilitates the attraction of the negatively charged peroxynitrite anion. Because the copper of superoxide dismutase is buried in a pocket shaped to accommodate superoxide, only peroxynitrite in the trans configuration should be able to fit in the active site. Because the predominant form of peroxynitrite is the cis form, the isomerization from the cis to trans geometry limits the reaction of peroxynitrite with superoxide dismutase. 

Bonifacic M, Schafer K, Mockel H, Asmus K-D (1975b) Primary steps in the reactions of organic disulfides with hydroxyl radicals in aqueous solution. J Phys Chem 79 1496-1502 Bonifacic M, Armstrong DA, Carmichael I, Asmus K-D (2000a) p-Fragmentation and other reactions involving aminyl radicals from amino acids. J Phys Chem B 104 643-649 Bonifacic M, Hug GL, Schoneich C (2000b) Kinetics of the reactions between sulfide radical cation complexes,[S.. S]+ and [S. N]+, and superoxide or carbon dioxide radical anions. J Phys Chem A 104 1240-1245... 

Bielski BFIJ, Shiue GG (1979) Reaction rates of superoxide radicals with the essential amino acids. In Oxygen free radicals and tissue damage. Ciba Foundation Symposium 65, Amsterdam, pp 43-56... 

Reaction Rate Constants of Superoxide Radical Anion/Perhydroxyl Radical with Amino Acids and Selected Antioxidants0... 

Pulse radiolysis investigations ofthe reaction of superoxide radical anions (O/ ) with radicals derived from various amino acids The following results were all obtained using pulse radiolysis. 

Superoxide dismutase (SOD) is a widely distributed enzyme that exists in a variety of forms. The copper-zinc enzyme (Cu,ZnSOD) is primarily located in the cytosol of eukaryotic cells. Mitochondria contain, in the matrix space, a distinctive cyanide-insensitive manganese-containing enzyme (MnSOD) similar to that found in prokaryotes. In addition, a ferrienzyme (FeSOD) has been identified in bacteria that is also insensitive to cyanide. Amino acid sequence homologies indicate two families of superoxide dismutases. One of these is composed of the Cu,ZnSODs and the other of MnSODs and FeSODs. All these superoxide dismutases catalyze the same reaction (2H -H O2 -h OJ H2O2 -t- O2) and with comparable efficiency. 

It is known that superoxide reacts very slowly with all amino-acids since all rate constants are below 100 mol l 1 s (89). Hence its reactivity with proteins without prosthetic group is low (89). One exception seems to be collagen, in which proline residues are oxidized into hydroxyproline (90). On the other hand, superoxide reacts efficiently with free radicals such as tryptophanyl radical (91). Reaction is fast with metalloproteins. It proceeds mostly by oxidizing or reducing the metal center. Some characteristics and rate constants of reactions with metalloproteins are given in table 7. It is obvious that products are often unknown and that the mechanism is sometimes unclear. It seems that there is no reaction with transferrin (92) and horseradish and lacto-peroxidase compounds II (93). The reason is unknown. 

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