The green microalga Lobosphaera incisa harbours an arachidonate 15 S ‐lipoxygenase

The green microalga Lobosphaera incisa is an oleaginous eukaryotic alga that is rich in arachidonic acid (20:4). Being rich in this polyunsaturated fatty acid ( PUFA ), however, makes it sensitive to oxidation. In plants, lipoxygenases ( LOX s) are the major enzymes that oxidise these molecules. Here, we describe, to our best knowledge, the first characterisation of a cDNA encoding a LOX (Li LOX ) from a green alga. To obtain first insights into its function, we expressed it in E. coli , purified the recombinant enzyme and analysed its enzyme activity. The protein sequence suggests that Li LOX and plastidic LOX s from bryophytes and flowering plants may share a common ancestor. The fact that Li LOX oxidises all PUFA s tested with a consistent oxidation on the carbon n‐6, suggests that PUFA s enter the substrate channel through their methyl group first (tail first). Additionally, Li LOX form the fatty acid hydroperoxide in strict S configuration. Li LOX may represent a good model to study plastid LOX , because it is stable after heterologous expression in E. coli and highly active in vitro . Moreover, as the first characterised LOX from green microalgae, it opens the possibility to study endogenous LOX pathways in these organisms.