Changes in Lipoxygenase Components of Rice Seedlings during Germination

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Abstract
Changes in lipoxygenase (LOX) activity were followed during the germination of rice seeds. The enzyme activity of 3-day-old seedlings was 20 times higher than that of ungerminated seeds. Sixty per cent of the increased activity was found in shoots. The increase in LOX activity was mainly due to an increase in lipoxygenase-2 (LOX-2), a minor component in ungerminated seeds; this increase was inhibited by cycloheximide. LOX-2 was isolated from the 3-day-old seedlings and compared for its enzymological properties with rice lipoxygenase-3 (LOX-3), a major component in ungerminated seeds. Both LOX-2 and LOX-3 were stable at pH 5 to 8, but LOX-2 was more heatstable than LOX-3. Apparent Km values of LOX-2 and LOX-3 for linoleic acid were 170 and 59 μM, and those for linolenic acid were 5,300 and 88 μM, respectively. Both LOXs were inhibited by some metal ions and antioxidants.