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Plant Physiology 48:19-23 (1971)
© 1971 American Society of Plant Biologists

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Articles

Isolation and Characterization of Polyphenol Oxidase Isozymes of Clingstone Peach 1

Thomas C. Wong2, Bor S. Luh and John R. Whitaker

a Department of Food Science and Technology, University of California, Davis, California 95616

The polyphenol oxidase system in clingstone peach (Prunus persica) was investigated. Polyacrylamide disc-gel electrophoresis indicated four bands with polyphenol oxidase activity in extracts from acetone powder of clingstone peach. These four isozymes were then isolated from a buffer extract of peach acetone powder by cold acetone precipitation, followed by diethylaminoethyl cellulose column chromatography. All isozymes had different heat stabilities. At 55 C, polyphenol oxidases A, B, and D had half-lives of 5.4, 14.6, and 14.1 minutes, respectively. Polyphenol oxidase C was stable over a period of 50 minutes of incubation at 55 C, but had a half-life of 2.2 minutes at 76 C. None of the isozymes had monophenolase activity, and they varied in their specificity for several diphenols. The following values were found for polyphenol oxidases A, B, C, and D, respectively, with catechol as substrate: optimal pH: 6.8, 6.5, 7.2, and 7.0; Michaelis constant: 6.6, 4.2, 7.0, and 36 mM; Vmax/(E0): 4.95, 39.4, 2.16, and 80.0 ({Delta}A min–1 mg–1). Each isozyme showed a different amount of inhibition by NaHSO3, NaCl, NaCN, L-ascorbic acid, glutathione, ethylenediaminetetraacetate, and sodium diethyldithiocarbamate.

2 Present address: Research Laboratory, E. & J. Gallo Winery, Modesto, Calif.

1 This investigation was supported in part by Training Grants UI-01053 and F & D-00008 from the United States Public Health Service. Taken from the dissertation submitted by Thomas C. Wong to the Graduate Division, University of California, Davis, in partial satisfaction of the requirements for the Ph.D. degree.






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Copyright © 1971 by the American Society of Plant Biologists