Omega-3 ( ω 3 or n -3) long-chain polyunsaturated fatty acids (PUFA), including eicosapentaenoic acid and docosahexaenoic acid (DHA), play physiologically important roles in vertebrates. These compounds have long been believed to have originated almost exclusively from aquatic (mostly marine) single-cell organisms. Yet, a recent study has discovered that many invertebrates possess a type of enzymes called methyl-end desaturases ( ω x ) that enables them to endogenously produce n -3 long-chain PUFA and could make a significant contribution to production of these compounds in the marine environment. Polychaetes are major components of benthic fauna and thus important to maintain a robust food web as a recycler of organic matter and a prey item for higher trophic level species like fish. In the present study, we investigated the ω x enzymes from the common ragworm, Hediste diversicolor , a common inhabitant in sedimentary littoral ecosystems of the North Atlantic. Functional assays of the H. diversicolor ω x demonstrated unique desaturation capacities. An ω 3 desaturase mediated the conversion of n -6 fatty acid substrates into their corresponding n -3 products including DHA. A further enzyme possessed unique regioselectivities combining both ω 6 and ω 3 desaturase activities. These results illustrate that the long-chain PUFA biosynthetic enzymatic machinery of aquatic invertebrates such as polychaetes is highly diverse and clarify that invertebrates can be major contributors to fatty acid trophic upgrading in aquatic food webs. This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers’: evidence and significance of consumer modification of dietary fatty acids’.

中文翻译：

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花叶草中发现的独特的脂肪酸去饱和酶能力说明了水生无脊椎动物在营养升级中的作用

欧米加3 （ω3 或n-3）长链多不饱和脂肪酸（PUFA），包括二十碳五烯酸和二十二碳六烯酸（DHA），在脊椎动物中发挥着重要的生理作用。长期以来，人们一直认为这些化合物几乎完全源自水生（主要是海洋）单细胞生物。然而，最近的一项研究发现，许多无脊椎动物拥有一种称为甲基末端去饱和酶的酶。ω X）使他们能够内源地生产n-3长链PUFA，可以为海洋环境中这些化合物的生产做出重大贡献。多毛类动物是底栖动物群的主要组成部分，因此作为有机物的回收者和鱼类等较高营养级物种的猎物，对于维持强大的食物网非常重要。在本研究中，我们调查了ω X来自普通沙蚕的酶，花叶荆，北大西洋沉积沿岸生态系统中的常见居民。的功能测定杂色 H. ω X表现出独特的去饱和能力。一个ω3 去饱和酶介导的转化n-6脂肪酸底物转化为相应的n-3种产品，包括DHA。另一种酶具有独特的区域选择性，结合了两者ω6 和ω3 去饱和酶活性。这些结果表明，多毛类等水生无脊椎动物的长链 PUFA 生物合成酶机制高度多样化，并阐明无脊椎动物可能是水生食物网中脂肪酸营养升级的主要贡献者。本文是主题“脂质作为‘营养生物标志物’的下一个前景：消费者改变膳食脂肪酸的证据和意义”的一部分。