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. 2016 Oct;57(10):1854–1864. doi: 10.1194/jlr.M070136

Fig. 1.

Fig. 1.

Two pathways for the biosynthesis of VLCPUFAs in Thraustochytrium sp. 26185. A: Aerobic pathway for biosynthesis of VLCPUFAs. The biosynthesis of VLCPUFAs in the aerobic pathway starts with 18:0 and goes through alternating desaturation and elongation steps. Three highlighted desaturases (Δ12, Δ6, and ω3) were new enzymes identified and functionally characterized by this study. The rest of the enzymes in the pathway were cloned and characterized previously from the species. No Δ9 desaturase sequence was detected in the Thraustochytrium genome and feed experiments did not observe the activity in the species. One Δ12 desaturase sequence was detected in the genome, however little activity was observed when it was expressed in yeast. In addition, feed experiments did not observe any Δ12 desaturation activity in vivo. B: Anaerobic pathway for biosynthesis of VLCPUFAs. The biosynthesis of VLCPUFAs in the anaerobic pathway starts with acetate and proceeds with reiterative cycles of four reactions: condensation by KS, ketoreduction (KR), dehydration (DH), and enoylreduction (ER). However, the synthesis may omit the certain last step of a full cycle, causing a double bond to be retained in the acyl chain.