Abstract:Tryptophane, tyrosine and phenylalanine are there kinds of fluorescent amino acids and exist in papain, so the structure change of papain can be measured by fluorescence spectra analysis without exterior fluorescence probe. Fluorescence excitation spectrum, emission spectrum and polarization spectrum were used to analyze the possible mechanisms of papain’s activity change after being treated by pulsed electric field (PEF). Results demonstrated that the relative activity of papain was decreased by 56.5% after PEF treatment under the condition of electric field strength 50 kV·cm-1,frequency 1 500 Hz, pulse width 40 μs and pulse number 19 800. The spectra of fluorescence excitation showed that the relative fluorescence strength of the treated sample was distinctly higher than the untreated one, even at peak position (280 nm) which was 80 and 120 for untreated and treated samples, respectively. The peak position in the fluorescence emission spectrum of treated sample was shifted from the original 342 nm to about 346 nm, and its fluorescence polarization degree was much smaller compared to the untreated sample. These phenomena indicated that the α-helix structure of papain was loosened or broken down after being treated by PEF. This treatment made the amino acid’s residue exposed from inside to outside, and even some fluorescent amino acids such as tryptophane, tyrosine and phenylalanine were decomposed from the α-helix structure of protein and went into the solution which helped increase the fluorescent strength. This effect led to the active site change of the enzyme and finally inactivated it.
Key words:Pulsed electric field;Papain;Activity of enzyme;Fluorescence spectrum
[1] Knorr D, Heinz V. Development of Nonthermal Methods for Microbial Control. In S. S. Block (Ed.), Disinfection, Sterilization, and Preservation). Philadelphia: Lippincott Williams & Wilkins, 2001. 853,877. [2] ZENG Xin-an, ZHANG Ben-shan, GENG Yu-huan(曾新安, 张本山, 耿予欢). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2002, 22(1): 29. [3] ZENG Xin-an, FU Xiong, LI Guo-ji, et al(曾新安, 扶 雄, 李国基, 等). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2004, 24(6): 748. [4] Van den Bosch H F M, Morshuis P H F, Smit J J. Proceedings of the IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2001. 552. [5] Zhang Q H. Barbosa-Canovas G V. Swanson B G. Journal Food Engineering,1995, 25: 261. [6] Mara L Calderon-Miranda, Gustavo V Barbosa-Canovas, Barry G Swanson. International Journal of Food Microbiology, 1995, 51: 7. [7] ZHANG Ying, ZENG Xin-an, ZHU Si-ming(张 鹰, 曾新安, 朱思明). Food Technology(食品科技), 2004, (3): 12. [8] XU Ya-li, ZENG Xin-an, YU Shu-juan(徐娅莉, 曾新安, 于淑娟). High Voltage Engineering(高电压技术), 2005, 31(12): 39. [9] Ho S Y, Mittal G S, Cross J D. Journal of Food Engineering, 1997, 31(1): 69. [10] Van Loey A, Verachtert B, Hendrickx M. Trends in Food Science and Technology, 2002, 12: 94. [11] Vega-Mercado H, Powers J R, Barbosa-Canovas G V, et al. Journal of Food Science, 1995, 60: 1143. [12] WANG Gui-hua, TAN Bing-he(王桂华, 谭秉和). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2002, 22(2): 328. [13] GU Song-hai, SONG Yi, LI Xu-hui(谷松海, 宋 义, 李旭辉). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2001, 21(3): 400. [14] Masatsugu Ken, Itoh Hiroshi. Regulatory Peptides, 2003, 111(3): 13.