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POLYPHENOL OXIDASE FROM BARHEE AND ZAHDI DATES. II. CHARACTERIZATION
Author(s) -
SACHDE ADIL G.,
ALBAKIR ALAA Y.,
ABDULRAHEEM JAMAL A. K.
Publication year - 1988
Publication title -
journal of food biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 47
eISSN - 1745-4514
pISSN - 0145-8884
DOI - 10.1111/j.1745-4514.1988.tb00376.x
Subject(s) - sodium metabisulfite , polyphenol oxidase , chemistry , uncompetitive inhibitor , ascorbic acid , catechol , catechol oxidase , oxalic acid , polyphenol , enzyme assay , cultivar , nuclear chemistry , sodium , enzyme , food science , non competitive inhibition , biochemistry , antioxidant , horticulture , organic chemistry , peroxidase , biology
Purified polyphenol oxidase (PPO) from Barhee and Zahdi date cultivars had a molecular weight of 17,500 and 17,000, respectively, as determined by exclusion gel chromatography. The enzyme possessed activity on o‐diphenols but not on monophenols or m‐diphenols. The highest activity was on catechol with K m of 3.5 and 8.75 mM for PPO from Barhee and Zahdi dates, respectively. PPO from the two cultivars showed optimal pH for activity and stability around 6.0 and 7.0, respectively. The enzyme was completely inactivated when incubated at 70°C for 10 min. Activation energy for conversion of substrate to product was 3400 and 3600 cal/mole for PPO from Barhee and Zahdi dates, respectively. However, the activation energy for denaturation was 28000 and 27000 cal/mole for the enzyme from Barhee and Zahdi cultivars, respectively. Ascorbic acid, oxalic acid and sodium metabisulfite caused non‐competitive inhibition for PPO activity, while sodium chloride was an uncompetitive inhibitor. Sodium metabisulfite was the most potent inhibitor with Ki values of 0.025 and 0.030 mM for PPO from Barhee and Zahdi dates, respectively.