Amino acids with peroxidized lipids

Table 3.37. Amino acid losses occurring in protein reaction with peroxidized lipids...

Table 3.38. Amino acid products formed in reaction with peroxidized lipid...

Hydroxyl radicals are the most reactive free-radical species known and have the ability to react with a wide number of cellular constituents including amino-acid residues, and purine and pyrimidine bases of DNA, as well as attacking membrane lipids to initiate a free-radical chain reaction known as lipid peroxidation. 

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,... 

In addition to cytochrome P-450 induction, other diet induced metabolic effects are likely to be involved in carcinogenesis. High temperature processing or long-term storage of foods with attendant exposure to oxygen can lead to the formation of lipid peroxides and oxidized sulfur amino acids in the food. The partially oxidized S-amino acids cystine monoxide (CMO) and methionine sulfoxide (MSO) are nutritionally available, but require in vivo conversion to the reduced amino acids at the... 

Experiments in vitro are consistent with some of the chemical investigations. Enzymes are readily inactivated by ozone, and the inactivation can be traced to the more susceptible amino acid residues (Table XI). Reactions with unsaturated fatty acids have been examined, and the production of malonaldehyde and hydrogen peroxide has been detected (52-54). The lipid products have not been analyzed, and the toxicity of such products is yet to be determined. 

Some amino acids may be oxidized by reacting with free radicals formed by lipid oxidation. Methionine can react with a lipid peroxide to yield methionine sulfoxide. Cysteine can be decomposed by a lipid free radical according to the following scheme ... 

Through their lipophilic nature the aldehyde lipid peroxidation products remain associated with the LDL particle, diffuse to the apoB and react there with amino-acid sidechains (for example epsilon amino groups of lysine). 

Peroxynitrite is a nonspecific oxidant that reacts with all classes of biomolecules depleting low-molecular-weight antioxidants, initiating lipid peroxidation, damaging nucleic acids and proteins. Its reactions are much slower than those of the hydroxyl radical but are faster than those of hydrogen peroxide. Comparison of peroxynitrite reactivity with various amino acid residues of human serum albumin have shown that cysteine, methionine, and tryptophan are the most reactive... 

A serious problem arises when lipids undergo peroxidation in the presence of protein. Free radicals originating from hydroperoxides transfer to several specific amino acid residues of protein. As a result, the protein undergoes radical induced polymerization, with loss of solubility and other original properties including nutritive value. 

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