Tea catechol oxidase: Isolation,purification and kinetic characterization |
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Authors: | Philip Coggon Gerald A Moss Gary W Sanderson |
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Institution: | Thomas J. Lipton, Inc., Englewood Cliffs, NJ 07632, U.S.A. |
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Abstract: | Cathechol oxidase extracted from tea leaves was purified over 200-fold, using isoelectric focusing. The purified catechol oxidase was free of peroxidase and flavanol gallate esterase activities. Further, this enzyme was shown to have optimum activity near pH 5·7 and a Km of 2·3 × 10?3 M (at 25°) for (?)-epigallocatechin gallate. The purified enzyme was found to be capable of epimerizing tea flavanols at their C-2 position whether oxidation of the flavanol occurs (aerobic conditions) or not (anaerobic conditions). When oxygen is present, gallic acid is formed as a result of oxidation of either (?)-epigallocatechin gallate or (?)-epicatechin gallate. Formation of gallic acid is a side reaction of the oxidation of the flavanol gallates and is named oxidative degallation; no esterase per se is involved in this reaction. |
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Keywords: | Theaceae tea catechol oxidase peroxidase galloyl esterase flavanol oxidation epimerization |
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