Superoxide dismutase,SOD) is an important component of antioxidant enzyme system in biological system, which is widely distributed in microorganisms, plants and animals[1]。
Superoxide Dismutase,SOD) is an antioxidant metalloenzyme existing in organisms, which can catalyze the disproportionation of superoxide anion free radicals to generate oxygen and hydrogen peroxide, plays a vital role in the balance between oxidation and antioxidant, and is inseparable from the occurrence and development of many diseases[2]。
classification
According to the different metal auxiliary groups in SOD, SOD can be roughly divided into three categories, namely Cu/Zn SODMn-SOD、 Fe-SOD[3]。
① Cu/Zn SOD: It is blue-green and mainly exists in the cytoplasm of eukaryotic cells. It is considered to exist in relatively primitive biological groups and has the widest distribution[3]。
② Mn SOD: pink, mainly present in the mitochondria of prokaryotes and eukaryotes[3]。
③ Fe SOD: It is yellowish brown and mainly exists in prokaryotic cells.They can effectively eliminate superoxide anion free radicals (with an unpaired electron and a negative charge), avoid excessive damage to cells, and have antioxidant, anti radiation, anti-aging and other functions[3]。
distribution
① Most primitive invertebrate cells contain Cu/Zn SOD, while vertebrates generally contain Cu/Zn SOD and Mn SOD.The red blood cells and liver cells of human, mouse, pig and cow contain Cu/Zn SOD, which mainly exists in the cytoplasm, but also between the inner and outer membranes of mitochondria.Mn SOD was also purified from human and animal hepatocytes, which generally existed in the mitochondrial matrix.
② Fe SOD in plant cells mainly exists in chloroplasts.
③ Fungi generally contain Mn SOD and Cu/Zn SOD.Most eukaryotic algae have Fe SOD in their chloroplast matrix, and Mn SOD is bound to the thylakoid membrane, while most algae do not contain Cu/Zn SOD.
structure
① Cu/Zn SOD: Its active center includes one Cu ion and one Zn ion.Research shows,The presence of Cu is necessary for the activity of Cu/Zn SOD. It directly interacts with superoxide anion free radicals. However, Zn is crowded around, not exposed directly in the reaction solution, and does not directly interact with superoxide anion free radicals, playing a role in stabilizing the surrounding environment of the active center.The divalent copper ion and the nitrogen atoms on the surrounding four histidine atoms are bound by coordination bonds, and the configuration is a distorted near plane square.There are three histidine around Zn which coordinate with it through nitrogen atom, and one histidine is shared by Cu and Zn, forming an "imidazole bridge" structure.In addition,Zn also coordinates with an aspartic acid residue, making Zn form a distorted tetrahedral coordination configuration[4]。
② Mn SOD: It is composed of 203 amino acid residues.The active center is Mn (Ⅲ), and the coordination structure is a five coordinated triangular bipyramid. One axial ligand is water molecule, the other axial coordinate is His-28 protein cofactor, and on the equatorial plane is His-83 protein cofactor,Asp-166 and His-170.The active site of the enzyme in an environment mainly composed of hydrophobic residues, two subunit chains form a channel, which forms the only way for the substrate or other internal ligand to approach Mn (Ⅲ) ion[5]。
reaction mechanism
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reaction mechanism
The catalytic action of SOD is through metal ion Mn+1(oxidized state) and Mn(reduced state) realized by alternating electron gain and loss.It is generally believed that superoxide anion radicals first form internal complexes with metal ions,Mn+1Reduced to M by superoxide anion free radicals in the bodyn, and generate O at the same timetwo，MnOnce again by HOtwo·Oxidation to Mn+1, and generate H at the same timetwoOtwo[3]。And SOD is oxidized to the initial oxidation state of SOD.last,HtwoOtwoUnder the action of catalase, it is catalysed to decompose into water (HtwoO) And Otwo[1]。
Determination method
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The main determination methods of superoxide dismutase activity include direct method, pyrogallol autoxidation method, cytochrome C reduction method, chemiluminescence method and fluorescence kinetics method.In recent years, many new methods have been established, such as immunological method, simple gel filtration diffusion method, polarographic oxygen electrode method, micro assay method, etc[2]。
1. The principle of direct method is based on O2.-Or generate O2.-Determination of O2.-To determine the activity of SOD.Classical direct methods include: pulse radiation decomposition methodElectron paramagnetic resonanceWave method (EPR)Nuclear magnetic resonance method。Because the required instruments and equipment are expensive, they are seldom used.
twoPyrogallolSelf oxidation method: the principle is based on the classicSpectrophotometry, under alkaline conditions,PyrogallolAutoxidation to citronellol, using UV-Visible spectrumThe tracking wavelength is 325nm, 420nm or 650nm (420nm in classic), and O2 is generated at the same time.-，SODcatalysisO2.-happenDisproportionation reactionThus, the autoxidation of pyrogallol is inhibited. The inhibition rate of the sample to the autoxidation rate of pyrogallol can reflect the SOD content in the sample.This method has the advantages of strong specificity, small sample size (only 50 μ l), fast and simple operation, good repeatability, high sensitivity, simple reagent, etc.
threeCytochrome CReduction method: the principle is xanthine-xanthine oxidaseO2 produced in the system.-Make a certain amount of oxidized typeCytochrome CIt is reduced to reduced cytochrome C, which has the largest light absorption at 550nm.In the presence of SOD, part of O2.-SODcatalysisAnd disproportionation,O2.-Cytochrome C reducingreaction rate The reaction is inhibited.The inhibition can be obtained by mapping the percentage of inhibition reaction with the concentration of SODcurveThus, the SOD activity in the sample is calculated.This method is a classical one among indirect methods, but its sensitivity is low.
fourChemiluminescence method: The principle isxanthine oxidaseUnder aerobic conditions,catalysisSubstrate xanthine orHypoxanthinehappenoxidation reaction Generate uric acid and O2 at the same time.-。The latter can be compared withChemiluminescent agentLuminol Reaction And make it generate excitation.SOD can remove O2.-So as to inhibitluminolChemiluminescence.This method can be applied to the micro determination of SOD. It is not only highly sensitive and simple, but also at least as specific and accurate asCytochrome CThe reduction method is similar.
5. Immunological method: it measures the activity of SOD. Immunological method can measure the quality of SOD in samples, so it has good specificity and is an ideal method for measuring SOD. Immunological methods include radioimmunoassay, chemiluminescence immunoassayELISAEtc.However, its defect is that it can only detect the antigen corresponding to the antibody. For the detection of different types of SOD, it is necessary to prepare the corresponding specific antibody, which is cumbersome.
application area
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Food
SOD content is high in vegetables and fruits, such as bananas, hawthorn, rosa roxburghii, kiwi fruit, garlic, etc., and others, such as scallops, chicken, etc.SOD activity was higher in peel than in pulp, and higher in fresh fruit than in placed fruit.It is processed into health products and food additives in various forms for use, such as milk, beer, soft candy and other food nutrition enhancers with SOD added[6]。
Daily chemical industry
Skin aging and injury are important characteristics of human aging, and human aging is the result of obstacles caused by accumulation or removal of reactive oxygen free radicals. Excess free radicals in the body will cause cell damage and pigmentation.As human skin directly contacts with oxygen, it will cause skin aging and damage.The supplement of exogenous SOD is conducive to delaying skin aging, anti-oxidation and removing color spots.Therefore, many cosmetics manufacturers at home and abroad have added a certain proportion of SOD to their products.For example, Estee Lauder pomegranate water in France, SKII fairy water in Japan, and Dabao SOD honey in China[1]。
Anti inflammatory aspects
Based on the fact that SOD is a specific disproportionation reaction catalyst acting on superoxide anion free radicals, SOD, as a medical product, has significant efficacy in treating inflammation, autoimmunity, cardiovascular and cerebrovascular diseases caused by free radicals.SOD can inhibit arthritis, pleurisy, acute tracheitis and other inflammatory types by its antioxidant effect[7]。
Reactive oxygen species, including superoxide free radicals, play an important role in colitis. Superoxide dismutase 1 (SOD1) can destroy superoxide free radicals in the body.A new study published on Redox Biology found that the loss of SOD1 can enhance the oxidative stress of mice, destroy the intestinal epithelial barrier, reduce the activity of antioxidant enzymes, increase the colonic infiltration of proinflammatory immune cells, and worsen DSS induced colitis in mice.The recovery of SOD activity can inhibit p38-MAPK/NF - κ B signal mediated inflammation and apoptosis, thereby alleviating colitis.[8]
Anti tumor
In human body, SOD can effectively eliminate superoxide anion free radicals and finally achieve the effect of inhibiting cancer cells,Mn SOD expression effect is more prominent[7]。
