Expression of Lipoxygenase and Hydroperoxide Lyase Activities in Tomato Fruits

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Abstract
The distribution (or locarization) of lipoxygenase (LOX) and hydroperoxide lyase (HPO lyase) activities in ripening and ripe tomato fruits was investigated. The highest LOX activity existed between skin and outer flesh of tomato fruits. HPO lyase showed no tissue specificity. LOX specifically formed linoleic acid 9-E, Z-hydroperoxide (9-E, Z-HPO) from linoleic acid (LA), whereas HPO lyase specifically cleaved 13-Z, E-HPO. Although a low level (0.36 ± 0.069 nmol/g fr. wt.) of hexanal was detected in the intact tomato fruit, HPOs were not detected. When a tomato fruit was injured by cutting it into 8 fragments and incubated at 25 °C, hexanal increased to 1.642 nmol/g fr.wt. by 30 min. By homogenizing at pH 6.3, hexanal increased to 21.1 nmol/g fr.wt. during a 30 min incubation. UV irradiation of tomato fruits also increased the formation of hexanal. From these results, LOX and HPO lyase are considered to exist as latent forms and to begin the expression of the activity upon injury.

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