Effect of pH on Circular Dichroism and Raman Spectroscopy of Secondary Structure of β-Casein from Chinese Human Milk
REN Hao-wei1,2, ZHANG Wan-shu1,2, LI Xiang-yi1,2, LIU Ning1,2,3*
1. National Dairy Engineering & Technical Research Centre，Heilongjiang Dairy Industry Technical Development Center, Harbin 150028, China 2. College of Food Science, Northeast Agricultural University，Key Laboratory of Dairy Science, Ministry of Education (Northeast Agricultural University), Harbin 150030, China 3. Synergetic Innovation Center of Food Safety and Nutrition, Harbin 150028, China
Abstract：To obtain a structural basis for the β-casein in Chinese human milk, structural transitions of the β-casein in response to variation of pH were investigated using Raman and circular dichroism (CD) spectroscopy. Both methods indicated that the secondary structures of β-casein in the solution were induced by the pH. Secondary structural analysis of β-casein by CD spectroscopy yielded 0.5%~2% α-helical, 16%~18% β-sheet, 30%~34% β-turn and 49%~51% random coil contents. Another result was that as pH increases, these structures change. Several distinct transitions were observed by circular dichroism in α-helix at pH 8 and pH 10. Raman spectrum also showed random coil as the major secondary structure in native β-casein, for the characteristic band of the β-casein amide I was at 1 662 cm-1. Calculations from I850/I830 suggested that the tyrosine residues of β-casein tended to “exposure”. CD and Raman spectra both showed that at neutral and alkaline pH the β-casein existed predominantly in random coil conformation, and the proportion of α-helix was higher at pH 8 than under other pH conditions. Over the range of pH studied, the sheet and turn areas remained relatively constant, and in the condition of pH 8, the content of α-helical was higher than in the other pH conditions.
任皓威1，2，张婉舒1，2，李相怡1，2，刘 宁1，2，3* . pH对中国人乳β-酪蛋白二级结构的圆二色和拉曼特征影响 [J]. 光谱学与光谱分析, 2015, 35(02): 384-389.
REN Hao-wei1,2, ZHANG Wan-shu1,2, LI Xiang-yi1,2, LIU Ning1,2,3* . Effect of pH on Circular Dichroism and Raman Spectroscopy of Secondary Structure of β-Casein from Chinese Human Milk . SPECTROSCOPY AND SPECTRAL ANALYSIS, 2015, 35(02): 384-389.
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