title: Comparison of membrane-bound and soluble polyphenol oxidase in Fuji apple (Malus domestica Borkh. cv. Red Fuji).
abstract: This study compared membrane-bound with soluble polyphenol oxidase (mPPO and sPPO, respectively) from Fuji apple. Purified mPPO and partially purified sPPO were used. mPPO was purified by temperature-induced phase partitioning and ion exchange chromatography. The specific activity of mPPO was 34.12× higher than that of sPPO. mPPO was more stable than sPPO at pH 5.0-8.5. Although mPPO was more easily inactivated at 25-55 °C, it is still more active than sPPO in this temperature range. The optimum substrate of mPPO was 4-methyl catechol, followed by catechol. L-cysteine had the highest inhibitory effects on mPPO followed by ascorbic acid and glutathione. Surprisingly, EDTA increased mPPO activity. The results revealed that purified mPPO is a dimer with a molecular weight of approximately 67 kDa.
authors.affiliation: College of Food Science and Nutritional Engineering, China Agricultural University, No. 17 Qinghua East Road, Beijing 100083, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Liu
authors.affiliation: College of Food Science and Nutritional Engineering, China Agricultural University, No. 17 Qinghua East Road, Beijing 100083, China.
authors.forename: Jin-Hong
authors.initials: JH
authors.lastname: Zhao
authors.affiliation: College of Food Science and Nutritional Engineering, China Agricultural University, No. 17 Qinghua East Road, Beijing 100083, China.
authors.forename: Zhi-Lin
authors.initials: ZL
authors.lastname: Gan
authors.affiliation: College of Food Science and Nutritional Engineering, China Agricultural University, No. 17 Qinghua East Road, Beijing 100083, China. Electronic address: niyycau@hotmail.com.
authors.forename: Yuan-Ying
authors.initials: YY
authors.lastname: Ni
mesh_terms: D004156:Catechol Oxidase / Q000737:chemistry* / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000201:enzymology*; D019281:Dimerization; D005638:Fruit / Q000737:chemistry / Q000145:classification / Q000201:enzymology; D007700:Kinetics; D027845:Malus / Q000737:chemistry / Q000145:classification / Q000201:enzymology*; D008970:Molecular Weight; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism; D012995:Solubility
chemical_list: D010940:Plant Proteins; D004156:Catechol Oxidase
keywords: Apple; Ascorbic acid; Polyphenol oxidase; Purification; l-cysteine