title: A comparative analysis of property of lychee polyphenoloxidase using endogenous and exogenous substrates.
abstract: Lychee polyphenoloxidase (PPO) was extracted and partially purified using ammonium sulphate precipitation and dialysis. The comparative analysis of PPO property was performed using its endogenous substrate (-)-epicatechin and exogenous substrate catechol. The pH optima for activity and activation temperature profiles of lychee PPO were very different when the enzyme reacted with endogenous and exogenous substrates. The addition of ethylenediaminetetraacetic acid disodium salt into the endogenous or exogenous substrate-enzyme system exhibited the same lowest inhibition of the PPO activity. However, l-cysteine was most effective in inhibiting enzymatic activity in the endogenous substrate-enzyme system while ascorbic acid was the best inhibitor in the exogenous substrate-enzyme system. Fe(2+) greatly accelerated the enzymatic reaction between endogenous substrate and PPO, but Cu(2+) exerted the same effect on the reaction between exogenous substrate and PPO. Based on the kinetic analysis, lychee PPO could strongly bind endogenous substrate but it possessed a higher catalytic efficiency to exogenous substrate.
authors.affiliation: South China Botanical Garden, The Chinese Academy of Sciences, 510650 Guangzhou, China; Guelph Food Research Center, Agriculture and Agri-Food Canada, Guelph, Canada N1G 5C9.
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
authors.affiliation: Guelph Food Research Center, Agriculture and Agri-Food Canada, Guelph, Canada N1G 5C9.
authors.forename: John
authors.initials: J
authors.lastname: Shi
authors.affiliation: College of Light Industry and Food Science, South China University of Technology, 510640 Guangzhou, China.
authors.forename: Mouming
authors.initials: M
authors.lastname: Zhao
authors.affiliation: Guelph Food Research Center, Agriculture and Agri-Food Canada, Guelph, Canada N1G 5C9.
authors.forename: Sophia Jun
authors.initials: SJ
authors.lastname: Xue
authors.affiliation: Guelph Food Research Center, Agriculture and Agri-Food Canada, Guelph, Canada N1G 5C9; College of Light Industry and Food Science, South China University of Technology, 510640 Guangzhou, China.
authors.forename: Jiaoyan
authors.initials: J
authors.lastname: Ren
authors.affiliation: South China Botanical Garden, The Chinese Academy of Sciences, 510650 Guangzhou, China. Electronic address: ymjiang@scbg.ac.cn.
authors.forename: Yueming
authors.initials: Y
authors.lastname: Jiang
keywords: Endogenous substrate; Exogenous substrate; Lychee; Polyphenol oxidase