中文摘要：

以蓝隐藻（Chroomonas placiodea）藻蓝蛋白PC-645为材料，通过改变环境pH和尿素质量浓度，监测其变性和复性过程中特征荧光谱和吸收谱的动力学变化，以期了解隐藻藻蓝蛋白的色基和蛋白结构稳定性及其与功能的关系。结果表明，PC-645在很宽的pH范围和一定质量浓度的尿素中维持结构和功能的稳定，空间结构具有很强的柔性。pH诱导的PC-645蛋白构象与功能变化可分为3个不同的区段。（1）稳定区（pH3．5～7）：吸收和荧光光谱都比较稳定，显示蛋白质构象和功能在此区域都保持正常。（2）a稳定区（pH7～10）：光吸收依然保持平稳，亚基内部的色基的状态和疏水微环境都没有改变，但荧光传递效率降低，可能是由亚基表面局部构象变化、解离（西级结构变化）或者色素基团间的空间距离变化引起。（3）不稳定区（pH〈3．5和pH〉10），吸光度和荧光强度都呈快速下降，色基在近紫外和可见光区的吸收峰位变动，蛋白构象处于快速崩溃期。PC-645在酸性条件下的稳定性高于在碱性环境下，是与隐藻藻蓝蛋白所处的特殊环境及生理功能相适应的。

英文摘要：

In this paper, we explored the structural stability of bilins as well as protein and functional variation of phycocyanin （PC） 645 from Chroomonas placoidea by means of monitoring the dynamic fluorescence and absorb- ance spectra during denaturation and renatuaration with different pH or different concentrations of urea. The results showed that PC-645 exhibited both structural and functional stability in wide range of pH and certain concentration of urea, which indicated a strong flexibility of three-dimensional structure of this protein. The pH-induced confor- mational and functional dynamics could be divided into three regions： （1） Stable region （pH 3.5 - 7）： in which both fluorescence and absorbance spectra were stable, presenting that the conformation together with the function of protein maintained normal. （2） Metastable region （pH 7-10）： absorbance spectra were still stable, which implied that the state ofbilins and hydrophobic micro-environment inside the subunits kept unchanged. But small amplitude of decrease of fluorescence transfer efficiency could be observed. This may be caused by local conformational changes on the surface of subunit, subunit dissociation or changes of distance among billins. （3） Unstable region （pH 〈 3 or pH 〉 10）： The fluorescent intensity and absorbance value decreased quickly, companied by absorption shifting of bilins at both near ultraviolet and visible region, which indicated rapid collapse of protein conformation. The result that PC-645 was more stable in acid condition than in alkali condition is in compliance with its distinct environment and physiological function.