Seiliez I, Panserat S, Corraze G, Kaushik S, Bergot P
Laboratory of Fish Nutrition, Unité mixte INRA-IFREMER, 64310, St-Pée-sur-Nivelle, France.
Comp Biochem Physiol B Biochem Mol Biol. 2003 Jul;135(3):449-60. doi: 10.1016/s1096-4959(03)00111-8.
Marine fish are presumed to have a lower capacity than freshwater fish for the bioconvertion of 18C fatty acids into 20-22C highly unsaturated fatty acids (HUFA). The present work investigated the first step of this pathway, the Delta6-desaturation, in gilthead seabream. A full-length desaturase-like cDNA was identified from total RNA extracted from viscera of juvenile fish fed for 96 days on an experimental HUFA-free diet containing olive oil as the sole lipid source. The open reading frame encodes a 445-amino acid peptide that contains two membrane-spanning domains, three histidine-rich regions, and a cytochrome b(5) domain, which are characteristic of Delta6- and Delta5-desaturases. Predicted protein sequence of seabream desaturase-like indicated a high percentage of identity with mammalian Delta6-desaturases (approx. 65%). Northern analysis showed two transcripts of approximately 3.7 and 1.8 kb which were highly expressed in fish fed on HUFA-free diet and slightly expressed in fish fed on HUFA-rich diet. The fatty acid profile of the former group was characterized by high levels of Delta6-desaturation products (18:2 n-9 and 20:2 n-9) with no detectable levels of Delta5-desaturation product (20:3n-9). These results demonstrate for the first time the presence and nutritional modulation of a Delta6-desaturase-like cDNA in a marine fish.
一般认为，海水鱼将18碳脂肪酸生物转化为20 - 22碳高度不饱和脂肪酸（HUFA）的能力低于淡水鱼。本研究以金头鲷为对象，对该途径的第一步——Δ6-去饱和作用进行了研究。从以橄榄油作为唯一脂质来源的无HUFA实验饲料喂养96天的幼鱼内脏中提取的总RNA中，鉴定出一个全长的类去饱和酶cDNA。该开放阅读框编码一个445个氨基酸的肽段，其包含两个跨膜结构域、三个富含组氨酸的区域以及一个细胞色素b5结构域，这些都是Δ6-和Δ5-去饱和酶的特征。金头鲷类去饱和酶的预测蛋白序列与哺乳动物的Δ6-去饱和酶具有较高的同源性（约65%）。Northern分析显示有两个转录本，大小约为3.7和1.8 kb，在喂食无HUFA饲料的鱼中高表达，而在喂食富含HUFA饲料的鱼中低表达。前一组的脂肪酸谱特征是Δ6-去饱和产物（18:2 n-9和20:2 n-9）水平较高，而未检测到Δ5-去饱和产物（20:3n-9）。这些结果首次证明了海水鱼中存在类Δ6-去饱和酶cDNA及其营养调控作用。
