Participation and Properties of Lipoxygenase and Hydroperoxide Lyase in Volatile C6-Aldehyde Formation from C18-Unsaturated. Fatty Acids in Isolated Tea Chloroplasts

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Abstract
Isolated tea chloroplasts utilized linoleic acid, linolenic acid and their 13-hydroperoxides as substrates for volatile C6-aldehyde formation. Optimal pH values for oxygen uptake, hydroperoxide lyase and the overall reaction from C18-fatty acids to C6-aldehydes were 6.3, 7.0 and 6.3, respectively. Methyl linoleate, linoleyl alcohol and γ-linolenic acid were poor substrates for the overall reaction, but linoleic and linolenic acids were good substrates. The 13-hydroperoxides of the above fatty acids and alcohol also showed substrate specificity similar to that of fatty acids. Oxygen uptakes (relative Vmax) with methyl linoleate, linoleyl alcohol, linolenic acid, γ-linolenic acid and arachidonic acid were comparable to or higher than that with linoleic acid. In winter leaves, the activity for C6-aldehyde formation from C18-fatty acids was raduced to almost zero. This was due to the reduction in oxygenation. The findings presented here provide evidence for the involvement of lipoxygenase and hydroperoxide lyase in C6-aldehyde formation in isolated chloroplasts.