Abstract
Polyphenol oxidase of Muscat Bailey A (Muscat Hamburg x Bailey) (MBA) was purified in a homogeneous form on SDS-PAGE and some of its properties were determined. The enzyme was extracted from the precipitate of MBA juice and purified by Sephadex G-100, hydroxyapatite, DEAE-Sepharose, and Ultrahydrogel 250 (HPLC) column chromatographies. The specific activity toward catechol increased 84-fold and the recovery was about 1%. The molecular weight of the enzyme was 40 kDa (SDS-PAGE) or 42 kDa (gel filtration). It had an optimum pH of 6.3 and was stable between pH 6 and 8. The optimum temperature for activity was 25°C to 30°C and the enzyme remained stable up to 30°C. When tested for substrate specificity, the enzyme catalyzed the oxidation of o-dihydroxy phenolic compounds but showed no activity toward monohydroxy phenols. The Km value toward catechol was 18.4 mM. Catecholase activity (browning activity) was well inhibited by ascorbic acid, potassium pyrosulfite, and other inhibitors, but the enzyme remained active in the presence of 1% SDS.
- Received March 1998.
- Revision received December 1998.
- Copyright 1999 by the American Society for Enology and Viticulture
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