On the reaction specificity of the lipoxygenase from tomato fruits

A lipoxygenase was purified 300-fold from a homogenate supernatant of ripe tomato fruits by fractionated ammonium sulfate precipitation and anion exchange fast protein liquid chromatography. The specific linoleate oxygenase activity of the final enzyme preparation was 1300 nkat per mg protein at pH 6.8 and 25 degrees C in the absence of any detergent. The enzyme oxygenated linoleic acid and alpha-linolenic acid at comparable rates, whereas gamma-linolenic acid, arachidonic acid, 11,14-eicosadienoic acid and 11,14,17-eicosatrienoic acid were poor substrates. Linoleic acid was converted to 9(S)-hydroperoxy-10E,12Z-octadecadienoic acid, whereas 5(S)-HpETE, 11(S)-HpETE and 8(S)-HpETE were identified as major oxygenation products from arachidonic acid. The tomato lipoxygenase did not react with either dilinoleyl phosphatidylcholine or the lipid extract from beef heart mitochondria. The possible biological importance of the reaction of tomato lipoxygenase with arachidonic acid is discussed.