pH值对丝素蛋白构象转变的影响

Influence of pH Value on the Conformation Transition of Silk Fibroin

模仿家蚕吐丝过程中伴随丝素蛋白自然脱水的纤维化过程 ,研究了再生丝素蛋白在各种 p H值的磷酸盐缓冲溶液体系中自然干燥脱水成膜后的构象转变 .利用激光拉曼散射光谱及其二维相关光谱 ,定性分析了丝素蛋白酰胺 区 ( 1 60 0～ 1 70 0 cm- 1 )散射峰的相关组成及结构 .在此基础上 ,利用 1 3C CP-MAS固体核磁共振谱对丝素蛋白丙氨酸 Cβ 峰 ( δ1 4.5～ 2 2 )进行了解析拟合 .从而确定了体系中与 Silk 及 Silk 构象相关的组成含量与 p H值的关系 .结果表明 ,p H=5 .2的酸性溶液有利于蚕丝丝素蛋白从 Silk 向 Silk 构象转变 ,而中性与碱性溶液 ( p H=6.9和 8.0 )

Both 13C CP-MAS solid state NMR and laser Raman scattering spectroscopy were used to investigate the influence of pH values on the conformation transition of silk fibroin of Bombyx mori silkworm. The regenerated silk fibroins in the phosphate buffer solution were used to imitate the silk fibroins of the gland. A series of membranes formed in buffer solutions with different pH values were obtained by the evaporation of water at room temperature(for mimicking the gradual loss of water in spinning process). The composes and conformation in the fibroin membranes were determined qualitatively by Raman and Generalized Two-Dimensional Correlation Raman Spectroscopy for amide Ⅰ region( 1 600—1 700 cm -1) of the silk fibroins. There are four types of conformations at least existing in the fibroin membranes, including conformations of typical silk Ⅰ(α-form and/or random coil), typical silk Ⅱ(β-sheet), silk Ⅰ transition and silk Ⅱ transition, etc.. Based on the qualitative results from 2D Raman spectrum, the relationship between pH value and conformation contents in the studied systems was determined quantitatively by simulation of C β peak (δ 14 5—22) in 13C CP-MAS solid state NMR spectrum. The results show that acidic solution(pH=5.2) is more favorable than neutral(pH=6.9) and basic(pH=8.0) ones for the conformation transition from Silk Ⅰ to Silk Ⅱ because the silk fibroin molecular backbones are easier to extend and then to form β-sheets in acidic solution.