Journal
PHYTOCHEMISTRY
Volume 101, Issue -, Pages 5-15Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.phytochem.2014.02.010
Keywords
Juglans regia; Type-3 copper protein; Polyphenol oxidase; Tyrosinase; Catechol oxidase; Laccase
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Funding
- University of Vienna [IK I041-N]
- Fonds zur Forderung der wissenschaftlichen Forschung (FWF) [P25217-N28]
- Austrian Science Fund (FWF) [P 25217] Funding Source: researchfish
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Polyphenol oxidase (PPO) is a type-3 copper enzyme catalyzing the oxidation of phenolic compounds to their quinone derivates, which are further converted to melanin, a ubiquitous pigment in living organisms. In this study a plant originated tyrosinase was isolated from walnut leaves (Juglans regia) and biochemically characterized. It was possible to isolate and purify the enzyme by means of an aqueous two-phase extraction method followed by chromatographic purification and identification. Interestingly, the enzyme showed a rather high monophenolase activity considering that the main part of plant PPOs with some exceptions solely possess diphenolase activity. The average molecular mass of 39,047 Da (Asp(101) --> Arg(445)) was determined very accurately by high resolution mass spectrometry. This proteolytically activated tyrosinase species was identified as a polyphenol oxidase corresponding to the known jrPPO1 sequence by peptide sequencing applying nanoUHPLC-ESI-MS/MS. The polypeptide backbone with sequence coverage of 96% was determined to start from Asp(101) and not to exceed Arg(445). (C) 2014 The Authors. Published by Elsevier Ltd.
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