Figure 3.

Identification of active lipoxygenases by MS/MS fragmentation of epoxyalcohols in C. closterium, N. shiloi and C. scutellum. For simplicity, the polyunsaturated chain of EPA is represented by the 1,3-pentadiene moiety that undergoes to enzymatic oxidation. R₁ and R₂ are variable alkyl residues to complement the structure of EPA (C20:5) or HTrA (C16:3). (a) Biosynthesis of fatty acids by LOX pathways; (b) MS parent ion and MS/MS fragmentation of epoxyalcohols analyzed as methyl esters in positive mode; (c) Diagnostic MS fragments used for the regiochemical identification of epoxyalcohols of diatoms. Assignments and abbreviations are in agreement with d’Ippolito et al. [34]. Structures are reported in Table S4 of the Supplementary Material.