Isolation and characterization of polyphenol oxidase isozymes of clingstone peach

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; V(max)/(E(0)): 4.95, 39.4, 2.16, and 80.0 (DeltaA min(-1) mg(-1)). Each isozyme showed a different amount of inhibition by NaHSO(3), NaCl, NaCN, l-ascorbic acid, glutathione, ethylenediaminetetraacetate, and sodium diethyldithiocarbamate.

Effect of Phloroglucinol and Resorcinol on the Clingstone Peach Polyphenol Oxidase-catalyzed Oxidation of 4-Methylcatechol

Phloroglucinol and resorcinol are not substrates for clingstone peach (Prunus persica) polyphenol oxidase, but they react with 4-methyl-o-quinone, produced either enzymatically or nonenzymatically, to give an intense red or red-brown color with a maximal absorption at about 470 nanometers. Several colored products were isolated from an ethyl acetate extract of the reaction by two-dimensional thin layer chromatography. Based on thin layer chromatographic and spectral studies of the enzymatic and nonenzymatic reactions, polyphenol oxidase does not play a role in the reaction between 4-methyl-o-quinone and phloroglucinol, resorcinol, d-catechin, or orcinol. In such reactions, the function of polyphenol oxidase is the formation of 4-methyl-o-quinone which then reacts nonenzymatically with the above phenols. Activation energies of both enzymatic and nonenzymatic reactions were determined.

The Effect of Bacterial Endotoxin on the Placenta of the Rat

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