| Superoxide dismutase (SOD, EC1.15.1.1) is one kind of metalloenzyme, which has been found ubiquitously among organisms. It could catalyse the dismutation of superoxide anion radical to molecular oxygen and hydrogen peroxide, clear superoxide anion radical and avoid the toxicity of active oxygen. It is one major of defense systems. SOD have some functions , such as defensing the toxicity of active oxygen, radiation-resistant, anti-aging, anti-tumor, anti-inflammation, and so on. So, it has fine foreground of development and application. According to the type of metal in the active site of the enzymes, SOD has been classified into four types: Cu/Zn-SOD, Mn-SOD, Fe-SOD, Ni-SOD. This text summarizes the research about SOD, such as type, distribution, physical and chemical characters, chemical structure, and the enzyme activity. There were many reports about SOD from plants and animals in the world, but no report about SOD from Ficus carica. Ficus carica is one of native health-care food. Such as strengthening spleen, promoting digestion, moistening the intestines, freeing the stool, reducing blood lipid, lowering blood pressure, detumescence, cancer prevention and antitumour. We had purified and characterized SOD from the Ficus carica leaves.Preserved Ficus carica leaves (150g) at -20℃were washed with distilled water precooled at 4℃, then were homogenized with sodium phosphate buffer. After extraction, ammonium sulfate classification, DEAE-Sepharose Fast Flow ion exchange chromatography and Sephacryl S-100 HR gel filtration chromatography successive steps purification, the purified enzyme was one protein band by PAGE . This explained that the purified SOD was homogeneous. Finally, SOD was 201-fold purified.SOD activity was assayed by the pyrogallol autoxidation method. One unit of SOD enzymatic activity was defined as the amount of enzyme inhibited the half of the rate of pyrogallol antoxidation per minute at 325 nm and 25℃. Protein concentration was determined by the Lowry's method using human serum albumin as the standard.Protein was visualized by staining with Coomassie brilliant blue R-250 when assayed with SDS-PAGE and SOD activity was negatively stained by riboflavin mediated photoreduction of Nitroblue Tetrazolium when assayed with PAGE.Cu/Zn-SOD and Fe-SOD are sensitive to hydrogen peroxide, but Mn-SOD is not. Cu/Zn-SOD is insensitive to the mixture of chloroform and ethanol, but Fe-SOD and Mn-SOD are not. According to its specific insensitivity to the mixture of chloroform and ethanol, it appeared to be Cu/Zn-SOD.The subunit molecular weight of the enzyme was determined by SDS-PAGE. The value was about 17,800 dalton. We estimated the value of the molecular weight of the enzyme was about 35,600 dalton.The experiments of dynamic properties investigated the effects of pH, temperature, chemical reagents and metal ions to SOD. The results show that the stability of this purified SOD is better than other enzymes. The optimum temperature and pH were 30℃and 6.0 respectively. The activity of the enzyme begin to lose when the temperature is over 70℃or pH is higher than 12.0. While the effect of hydrogen peroxide was very obvious, the effects of other chemical reagents, such as NaN3, SDS,β-mercaptoethanol, urea and trypsinase on the activity of SOD were not obvious. Ultraviolet absorption spectrum showed that the maximum absorbance apex of the purified SOD was at 278 nm. The content ofα-helix of the enzyme was approximate 12.78% according to circular dichroism spectrum. Fluorescence spectrum examination showed that the maximum emission wavelength of the enzyme was 338 nm.
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