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Ellagic acid: Characterization as substrate of polyphenol oxidase
Author(s) -
MuñozMuñoz Jose Luis,
GarciaMolina Francisco,
GarciaMolina Maria,
Tudela Jose,
GarcíaCánovas Francisco,
RodriguezLopez Jose Neptuno
Publication year - 2009
Publication title -
iubmb life
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.132
H-Index - 113
eISSN - 1521-6551
pISSN - 1521-6543
DOI - 10.1002/iub.143
Subject(s) - ellagic acid , polyphenol oxidase , chemistry , substrate (aquarium) , antioxidant , polyphenol , tyrosinase , radical , enzyme , oxidase test , biochemistry , stereochemistry , organic chemistry , biology , peroxidase , ecology
Ellagic acid has been described as an inhibitor of tyrosinase or polyphenol oxidase and, therefore, of melanogenesis. In this work, we demonstrate that ellagic acid is not an inhibitor, but a substrate of mushroom polyphenol oxidase, an enzyme which oxidizes ellagic acid, generating its o ‐quinone. Because o ‐quinones are very unstable, we used an oxymetric method to characterize the kinetics of this substrate, based on measurements of the oxygen consumed in the tyrosinase reaction. The catalytic constant is very low at both pH values used in this work (4.5 and 7.0), which means that the Michaelis constant for the oxygen is low. The affinity of the enzyme for the substrate is high (low K m S ), showing the double possibility of binding the substrate. Moreover, a new enzymatic method is applied for determining the antioxidant activity. Ellagic acid shows high antioxidant activity (EC50 = 0.05; number of electrons consumed by molecule of antioxidant = 10), probably because of the greater number of hydroxyl groups in its structure capable of sequestering and neutralizing free radicals. © 2008 IUBMB IUBMB Life, 61(2): 171–177, 2009