| 摘要: |
| 采用不同光照条件、不同浓度的十二烷基硫酸钠（SDS)和脲，以及不同pH等条件处理钝顶螺旋藻别藻蓝蛋白(APC)，检测其光谱变化、生成及清除自由基能力的变化，对纯化的钝顶螺旋藻别藻蓝蛋白(APC)在不同条件下的抗氧化活性进行了研究。结果表明，光照下，APC具有生成自由基的能力；黑暗中，APC却表现为清除自由基。SDS是一种很强的变性剂，1mmol/L的SDS即可以使APC完全变性，能量传递功能丧失，光照下，APC生成自由基的能力丧失，自由基清除能力明显增强。1.6mol/L的脲作用后，只使APC部分变性，导致APC能量传递效率降低，光照下，表现为生成自由基的能力下降。随着脲浓度的升高(3.2mol/L、6.4mol/L)，APC的结构逐渐变化，能量传递功能逐渐丧失，表现为生成自由基的能力逐渐下降，清除自由基的功能逐渐增强。APC具有较宽的pH稳定性，在pH为7–1.0的范围内非常稳定；当pH为1.1时，APC的结构已经发生变化。在日光灯下，pH为7时，APC具有生成自由基的能力；pH为8时，APC的荧光光谱虽然没有发生变化，但它们表现为清除自由基的能力。随着pH的增加，自由基清除能力也增强。因此，APC具有产生和清除自由基的双重功能，光照是调控自由基清除与产生的关键因素，并且只有APC具有能量吸收和传递功能时，才具有产生自由基的能力。脱辅基蛋白变性后，清除自由基的能力加强。 |
| 关键词: 钝顶螺旋藻 别藻蓝蛋白 脱辅基蛋白 抗氧化剂 |
| DOI： |
| 分类号: |
| 基金项目:国家高技术发展计划“863计划”资助项目，2002AA302213号；山东省自然科学基金资助项目，031070113号；山东省科技发展计划资助项目，031070113号 |
附件 |
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| EFFECTS OF LIGHT, DENATURANTS AND pH ON ANTIOXIDANT ACTIVITY OF APC IN BLUE GREEN ALGA SPIRULINA PLATENSIS |
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ZHOU Zhan-Ping1, LIU Lu-Ning1, CHEN Xiu-Lan1, ZHANG Xi-Ying1, ZHANG Yu-Zhong1, ZHOU Bai-Cheng2
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1.State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100;2.Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071
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| Abstract: |
| Phycobilisomes are protein complexes that function in light harvesting and energy migration, usually to photosystem II. Biliproteins consist of apoproteins as well as chromophores, which are observed to be singly or doubly attached by thioether bonds to cysteine residues of the apoproteins. Previous articles thought that the chromophore plays an important role in the ability of scavenging hydroxyl radicals of the phycobiliprotein.
In this study, allophycocyanin (APC) purified from blue green alga Spirulina platensis was treated in different light conditions, SDS and urea with different concentrations, and by buffer of different pHs. Then their fluorescence spectra, and ability of generating and scavenging hydroxyl radicals were detected. Results showed that:(1) the natural APC could generate hydroxyl radicals in light and scavenge them in darkness; (2) SDS was strong denaturant1 C-phycocyanin( CPC) and APC denatured completely in 1mmol/ L SDS. They were not be able to absorb and transfer the light energy. The ability of generating hydroxyl radicals disappeared in light and the ability of scavenging hydroxyl radicals increased remarkably; (3) after denatured partly in 1.6mol/L urea, APCs were still able to absorb and transfer energy, but the efficiency and their ability of generating hydroxyl radicals decreased. APCs denatured more with rising (3.2mol/L, 6.4mol/L) concentration of urea. It scavenged hydroxyl radicals instead of generating them; (4) APCs could stabilize in a wide range of pH between 7–10. In pH 11 the structure of APC changed1 APCs had an ability to generate hydroxyl radicals in pH 7 in light. Their fluorescence spectrum did not change in pH 8 but scavenged hydroxyl radicals. This ability increased with pH increasing.
The spectroscopic properties of phycobiliprotein depend on the chemical structure of the bilins they contain and on the conformation and environment imposed on these bilins by the native protein structure. The spectral characterization of APC was determined by its advanced structure. The chromophore of APC plays a key role in the spectral characterization. At the same time, the microenvironment of apoprotein affects the natural ability of the chromophore and change the spectral identity of the whole protein. This article studied the antioxidant act ivities of APC in different conditions. The phycobiliprotein was processed in different conditions in which various spectral characterization and antioxidant ability were shown. In all, it is indicated in this paper that natural state of the phycobiliprotein benefit for the absorbance and transfer of the light, rather than the ability of scavenging hydroxyl radicals. APCs have dual abilities of generating and scavenging hydroxyl radical during these process the light condition is the key. When APC absorb and transfer energy, it generates hydroxyl radicals. When apoprotein denatures, APC′s ability of scavenging hydroxyl radicals increases. |
| Key words: Spirulina platensis, APC, Apoprotein, Antioxidant |
