Journal
FOOD CHEMISTRY
Volume 117, Issue 2, Pages 342-348Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.foodchem.2009.04.013
Keywords
Polyphenol oxidase; Red Swiss chard; Purification; Characterisation; Diphenolase
Funding
- Chinese High-Tech RD [2008AA10Z103]
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We report purification and characterisation of a polyphenol oxidase from red Swiss chard (rcPPO). Our purification procedure resulted in a 39-fold enrichment in specific activity and 17% recovery of total enzyme activity. The purified rcPPO appeared as a monomeric protein of 41 kDa, with a specific conformation conserved in the Cu2+ combining region. It was optimally active at pH 7.5 and 45 degrees C. It had a diphenolase substrate preference towards L-DOPA, catechol and chlorogenic acid, but also exhibited weak monophenolase one toward 4-methoxyphenol and L-tyrosine. We also found that the enzyme was activated by K+, Na+, SDS and laurouyl sarcosine, but inhibited by divalent cations including Ca2+, Cu2+. Its activity was completely inhibited by ascorbic acid, cysteine, 1,4-dithiothreitol, beta-mercaptoethanol, sodium diethyldithiocarbamate, sodium metabisulphite, sodium sulphite and thiourea. This first report on the purification and characterisation of red Swiss chard PPO provides a basis for understanding and use of this enzyme. (C) 2009 Elsevier Ltd. All rights reserved.
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