In addition, there are compounds that have a relatively low specific antioxidative activity, i.e., on a molar basis, but, when present at high concentrations, can contribute significantly to the overall ROS scavenging activity. The most prominent examples of such high-level, low-efficiency antioxidants are free amino acids, peptides, and proteins. Practically all amino acids can serve as targets for oxidative attack by ROS, although some amino acids such as tryptophan, tyrosine, histidine, and cysteine are particularly sensitive to ROS (126, 128,545). Because the cumulative intracellular concentration of free amino acids is on the order of 10−1 M, free amino acids are quantitatively important ROS scavengers (see sect.III B5)..
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