Abstract
In view of the great importance bestowed on amino acids as antioxidants in oxidation resistance, we attempted two common redox titration methods in this report, including micro-potassium permanganate titration and iodometric titration, to measure the antioxidative capacity of 20 amino acids, which are the construction units of proteins in living organisms. Based on the relative intensities of the antioxidative capacity, we further conducted a quantitative comparison and found out that the product of experimental values obtained from the two methods was proven to be a better indicator for evaluating the relative antioxidative capacity of amino acids. The experimental results were largely in accordance with structural analysis made on amino acids. On the whole, the 20 amino acids concerned could be divided into two categories according to their antioxidative capacity. Seven amino acids, including tryptophan, methionine, histidine, lysine, cysteine, arginine and tyrosine, were greater in total antioxidative capacity compared with the other 13 amino acids.
Highlights
Oxidation resistance, as a normal, unavoidable and indispensable physiological process, plays a positive role in maintaining homeostasis in living organisms
We clearly know a variety of anti-oxidizing systems present in living organisms, and they include some enzymes, such as superoxide dismutase, catalase and glutathione peroxidase, etc. [1,2,3], various proteins, such as albumin, ceruloplasmin, ferritin, etc. [4,5,6], many compounds of relatively small molecules, such as ascorbic acid, α-tocopherol, β-carotene, ubiquinol-10, glutathione (GSH), methionine, uric acid, bilirubin [7,8,9] and hydroxytyrosol, etc. [10,11], and some hormones, such as estrogen, angiotensin and melatonin, etc. [12,13,14]
Sodium oxalate, iodine, potassium iodide, potassium dichromate and sodium thiosulfate were of analytical grade, and the 20-amino acid kit was obtained from Accustandard (New Haven, CT, USA)
Summary
As a normal, unavoidable and indispensable physiological process, plays a positive role in maintaining homeostasis in living organisms. When oxidation resistance surpasses the organism’s immune burden, it will definitely bring detrimental consequence to the organism, even triggering various chronic, even life-threatening diseases. We clearly know a variety of anti-oxidizing systems present in living organisms, and they include some enzymes, such as superoxide dismutase, catalase and glutathione peroxidase, etc. The vital important role of antioxidants in healthcare and disease prevention lead many researchers to the investigation of the antioxidative capacity of various bioactive substances, such as plants [15], animal proteins [16] and several amino acids [17]. To be accurate, alpha-amino acids, the building blocks of proteins in living organisms, naturally attract researchers’
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