| Free radicals are the dissociated molecules, atoms or ions with unpaired electron, having an active chemical property. Under the physiological condition, the concentration of free radicals, occupying the state of equilibrium, is very low. Not only do they not damage the organism, but also have some special physiological functions. Under the pathological condition, free radicals generated by physical factor and xenobiotics directly or indirectly cannot be scavenged in time or the equilibrium of producing and scavenging endogenous free radicals is broken, then the body is injured by free radicals.Because of the damage by free radicals, it is extremely necessary to scavenge oxygen free radical as well as derivates. There are two kinds of the scavengers for free radicals in the organism, namely enzymes (Anti-oxidative enzymes) and non-enzyme compounds. The enzyme scavengers mainly include SOD, CAT and GPX, and they form the defense system in the organism against free radicals. In addition, many small molecular compounds also have strong anti-oxidative ability. These compounds are vitamin C, vitamin E,α-tocopherol, reduced glutathione,β-carotene, metal chelate complex, calcium ion antagonists, flavonoid, polyphenol compouns and antioxidant peptides, and so on. Together with antioxidant enzymes they make free radicals be in below the normal level of metabolism in organism.GPX are the well-known antioxidant seleno-enzymes in organisms which destroy several harmful hydro peroxides and then maintain the metabolic balance of ROS in vivo, thus protecting the bio-membranes and other cellular components from oxidative damage. In certain pathogenic states, the production of ROS is enhanced and the excess ROS damage various bio-macromolecules including RNA, DNA, protein, sugars and lipids, and therefore result in ROS-mediated diseases. ROS-related diseases include reperfusion injury, inflammatory process, age-related diseases, neuronal apoptosis, cancer and cataract. Therefore, GPX can really act as antioxidant drugs.It is possible to develop potent antioxidant drugs and functional foods through studying and separating some natural goods which have anti-oxidative activity. Due to high output and low cost of soy, it has been one of the important foods. Hence, there is important social significance and economic value to study and develop soybean peptides with anti-oxidative activity. This research starts with hydrolyzing Soybean Isolated Protein (SPI) by Alcalase for 5 hours. The hydrolyzed SPI was separated into two parts by using Sephadex G-25 gel filtration chromatography. We got SPI-H-1 which is larger than 2000 Da, and SPI-H-2 which is smaller than 2000 Da. By adding selenium atom (Se) on the–OH of cysteine, we got SPI-H-Se-1 (Selenium-Containing SPI hydrolysis) and SPI-H-Se-2. The GPX activity per selenium-containing peptide molecular of SPI-H-Se-1 is 3.72×102 U/μmol, and that of SPI-H-Se-2 is 3.72×102 U/μmol.The pyrogallic acid auto-oxidation system is performed to research the ability to scavenge superoxide anion. The result showed that on the concentration of 1.0 mg/ml, the inhibition ratio to pyrogallic acid auto -oxidation of SPI-H-Se-2 reaches 38.4%, which is 19% than the inhibition ratio of SPI-H-2 and SPI-H-Se-1.Fenton/Rh-B-induced damage system indicated that all of Soybean Peptide SPI-H-2 and Se-Soybean-Peptide SPI-H-Se-1, SPI-H-Se-2 can effectively scavenge·OH. Among them, SPI-H-Se-1 shows the highest scavenging efficiency, which scavenged 95.8% of all the·OH on the concentration of 167μg/ml. SPI-H-Se-1 raise its efficiency 95% of SPI-H-2's on the concentration of 83μg/ml.We also investigated the antioxidant ability of the peptides by using mitochondria injury system. The result showed that when GSH is added to the system, SPI-H-Se-2 can protect mitochondria from injury much better than SPI-H-2. But when GSH is absence, the abilities of protecting mitochondria are quite near.This result indicates that the anti-oxidative activity of Soybean Peptides is efficiently raised by obtaining GPX activity as GSH is often existed in vivo.
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