substrates and carboxylic acid inhibitors of a partially purified polyphenol oxidase from gum arabic
Journal of Agricultural and Food Chemistry, ISSN: 0021-8561, Vol: 44, Issue: 7, Page: 1668-1675
1996
- 23Citations
- 13Captures
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Article Description
Polyphenol oxidase (PPO) was extracted from gum arabic, and two isoenzymes were partially purified by ammonium sulfate treatment and hydrophobic and ion-exchange chromatographies. Both fractions displayed an optimum at pH 5.3. PPOs showed activity toward o-diphenolic substrates but not on monophenols or p-diphenols. Activity was maximum with 4-methylcatechol (4MC) followed by the two catechins. Both enzymes showed apparent K of 0.8 mM for (+)-catechin and 2.4 mM for (-)-epicatechin and 4MC. Aromatic acids of the benzoic, cinnamic, and phenylalkanoic series and sorbic acid were mixed-type inhibitors. Benzoic acid was the most effective one (K = 0.44 mM and K′ = 1.3 mM). Inhibition efficiency increased when pH was lowered indicating that both neutral (AH) and dissociated (A) forms are responsible for inhibition. For all compounds tested, AH forms were more potent inhibitors than A forms, and their affinity was higher for free enzyme than for the complex enzyme-substrate.
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