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Characterization of germin-like protein with polyphenol oxidase activity from Satsuma mandarine
Authors:Xi Cheng  Xingjian HuangSiyu Liu  Mi TangWanfeng Hu  Siyi Pan
Affiliation:College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China; Key Laboratory of Environment Correlative Dietology (Huazhong Agricultural University), Ministry of Education, China
Abstract:
Polyphenol oxidases (PPOs) catalyzing the oxygen dependent oxidation of phenols to quinones are ubiquitously distributed in plants and are assumed to be involved in plant defense against pests and pathogens. A protein with high PPO activity was identified in Satsuma mandarine, extracted with Tris–HCl buffer, purified by salt precipitation and column chromatography, and characterized by mass spectrometry as germin-like protein (GLP), which belongs to pathogenesis related protein (PR) family. In the present study, the structure and enzymatic properties of GLP were characterized using spectroscopy methods. Based on native PAGE analysis, the molecular weight of GLP was estimated to be 108 kDa and GLP was identified as a pentamer containing five subunits of 22 kDa. The optimum pH and temperature for PPO catalyzing activity of GLP was 6.5 and 65 °C, respectively. Kinetic constants were 0.0365 M and 0.0196 M with the substrates catechol and pyrogallol, respectively. The structural characterization of GLP provided better insights into the regions responsible for its PPO activity.
Keywords:GLP, germin-like protein   PPO, polyphenol oxidase   SOD, superoxide dismutase   PR, pathogenesis-related protein   CD, circular dichroism spectrum   PSD, particle size distribution   DSL, dynamic light scattering   Tris, tris(hydroxymethyl)aminomethane   PVPP, cross linking polyvinylpyrrolidone
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