We determined the molecular weight and some properties of multiple forms of phenol oxidase from tea leaves and four other perennial plants. It was shown that multiple high and low molecular forms of phenol oxidase differed in substrate specificity. Low molecular forms of the enzyme mostly demonstrated hydroxylase activity, while high molecular forms showed catechol oxidase activity. It was revealed that the withering stage of black tea production is accompanied by the formation of only high molecular forms of phenol oxidase, which possess catechol oxidase activity crucial for the procurement of oxidative reactions and the quality of the product.

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Stabilities of phenol oxidase and peroxidase from tea plant ( Camellia sinensis L.) clone Kolkhida leaves, apple ( Mallus domestica L.) cultivar Kekhura fruits, walnut ( Juglans regia L.) green pericarp, and horseradish ( Armoracia lapathifolia Gilib) roots were studied using different storage temperature modes and storage duration. It was demonstrated that both enzymes retained residual activities ( ~10% ) upon 20-min incubation at 80 ° C. Phenol oxidases from tea, walnut, and especially apple, as well as tea peroxidase, were stable during storage. A technology for the treatment of plant oxidases was proposed, based on the use of a natural inhibitor of phenol oxidase and peroxidase, isolated from tea leaves, which solves the problem of residual activities of these enzymes that arises during pasteurization and storage of beverages and juices. It was demonstrated that browning of apple juice during pasteurization and beer turbidity during storage could be efficiently prevented using the natural inhibitor of these enzymes.

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Novel tea catechin derivatives have been synthesized, and a structure-activity study, related to the capacity of these and other polyphenols to bind dihydrofolate reductase (DHFR), has been performed. The data showed an effective binding between all molecules and the free enzyme, and the dissociation constants of the synthetic compounds and of the natural analogues were on the same order. Polyphenols with a catechin configuration were better DHFR inhibitors than those with an epicatechin configuration. Antiproliferative activity was also studied in cultured tumour cells, and the data showed that the activity of the novel derivatives was higher in catechin isomers. Derivatives with a hydroxyl group para on the ester-bonded gallate moiety presented a high in vitro binding to DHFR, but exhibited transport problems in cell culture due to ionization at physiologic pHs. The impact of the binding of catechins to serum albumin on their biological activity was also evaluated. The information provided in this study could be important for the design of novel medicinal active compounds derived from tea catechins. The data suggest that changes in their structure to avoid serum albumin interactions and to facilitate plasmatic membrane transport are essential for the intracellular functions of catechins.