The synthetic pathways responsible for the production of the polyunsaturated fatty acids 22:6n-3 and 20:5n-3 were studied in the Dinophyte Alexandrium minutum. The purpose of this work was to follow the progressive incorporation of an isotopic label (¹³CO₂) into 11 fatty acids to better understand the fatty acid synthesis pathways in A. minutum. The Dinophyte growth was monitored for 54 hours using high-frequency sampling. A. minutum presented a growth in two phases. A lag phase was observed during the first 30 hours of development and had been associated with the probable temporary encystment of Dinophyte cells. An exponential growth phase was then observed after t₃₀. A. minutum rapidly incorporated ¹³C into 22:6n-3, which ended up being the most ¹³C-enriched polyunsaturated fatty acid (PUFA) in this experiment, with a higher ¹³C atomic enrichment than 18:4n-3, 18:5n-3, 20:5n-3, and 22:5n-3. Overall, the ¹³C atomic enrichment (AE) was inversely proportional to number of carbons in n-3 PUFA. C₁₈ PUFAs, 18:4n-3, and 18:5n-3, were indeed among the least ¹³C-enriched FAs during this experiment. They were assumed to be produced by the n-3 PUFA pathway. However, they could not be further elongated or desaturated to produce n-3 C₂₀-C₂₂ PUFA, because the AEs of the n-3 C₁₈ PUFAs were lower than those of the n-3 C₂₀-C₂₂ PUFAs. Thus, the especially high atomic enrichment of 22:6n-3 (55.8% and 54.9% in neutral lipids (NLs) and polar lipids (PLs), respectively) led us to hypothesize that this major PUFA was synthesized by an O₂-independent Polyketide Synthase (PKS) pathway. Another parallel PKS, independent of the one leading to 22:6n-3, was also supposed to produce 20:5n-3. The inverse order of the ¹³C atomic enrichment for n-3 PUFAs was also suspected to be related to the possible β-oxidation of long-chain n-3 PUFAs occurring during A. minutum encystment.

中文翻译：

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使用 13C 标记鉴定有毒 Dinophyte Alexandrium minutum 中的多不饱和脂肪酸合成途径

在 Dinophyte Alexandrium minutum中研究了负责产生多不饱和脂肪酸 22:6n-3 和 20:5n-3 的合成途径。这项工作的目的是跟踪同位素标记 ( ¹³ CO ₂ ) 逐渐纳入 11 种脂肪酸，以更好地了解A. minutum 中的脂肪酸合成途径。使用高频采样监测恐龙植物的生长 54 小时。A. minutum呈现出两个阶段的增长。在发育的前 30 小时内观察到一个滞后期，这与可能的 Dinophyte 细胞的临时包囊有关。然后在 t ₃₀之后观察到指数生长期。A. minutum迅速将¹³ C结合到 22:6n-3 中，最终成为本实验中富含¹³ C 的多不饱和脂肪酸 (PUFA)，其¹³ C 原子含量高于 18:4n-3、18： 5n-3、20:5n-3 和 22:5n-3。总体而言，¹³ C 原子富集 (AE) 与 n-3 PUFA 中的碳数成反比。C ₁₈ PUFA、18:4n-3 和 18:5n-3 确实是该实验中最少¹³种富含 C 的 FA 之一。假设它们是由 n-3 PUFA 途径产生的。然而，它们不能进一步延长或去饱和以产生 n-3 C ₂₀ -C ₂₂ PUFA，因为 n-3 C ₁₈的 AEPUFAs 低于n-3 C ₂₀ -C ₂₂ PUFAs。因此，特别高的 22:6n-3 原子富集（中性脂质 (NL) 和极性脂质 (PL) 分别为 55.8% 和 54.9%）使我们假设这种主要的 PUFA 是由不依赖O _{2 的}聚酮合酶 (PKS) 途径。另一个并行 PKS，独立于导致 22:6n-3 的那个，也应该产生 20:5n-3。n-3 PUFA的¹³ C 原子富集的相反顺序也被怀疑与A. minutum包囊过程中发生的长链 n-3 PUFA 可能的 β-氧化有关。