Yoshinaga Naoko, Aboshi Takako, Abe Hiroaki, Nishida Ritsuo, Alborn Hans T, Tumlinson James H, Mori Naoki
Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
Proc Natl Acad Sci U S A. 2008 Nov 18;105(46):18058-63. doi: 10.1073/pnas.0809623105. Epub 2008 Nov 7.
Since the first fatty acid amino acid conjugate (FAC) was isolated from regurgitant of Spodoptera exigua larvae in 1997 [volicitin: N-(17-hydroxylinolenoyl)-L-glutamine], their role as elicitors of induced responses in plants has been well documented. However, studies of the biosyntheses and the physiological role of FACs in the insect have been minimal. By using (14)C-labeled glutamine, glutamic acid, and linolenic acid in feeding studies of Spodoptera litura larvae, combined with tissue analyses, we found glutamine in the midgut cells to be a major source for biosynthesis of FACs. Furthermore, 20% of the glutamine moiety of FACs was derived from glutamic acid and ammonia through enzymatic reaction of glutamine synthetase (GS). To determine whether FACs improve GS productivity, we studied nitrogen assimilation efficiency of S. litura larvae fed on artificial diets containing (15)NH(4)Cl and glutamic acid. When the diet was enriched with linolenic acid, the nitrogen assimilation efficiency improved from 40% to >60%. In the lumen, the biosynthesized FACs are hydrolyzed to fatty acids and glutamine, which are reabsorbed into tissues and hemolymph. These results strongly suggested that FACs play an active role in nitrogen assimilation in Lepidoptera larva and that glutamine containing FACs in the gut lumen may function as a form of storage of glutamine, a key compound of nitrogen metabolism.
自1997年首次从甜菜夜蛾幼虫的反流物中分离出第一种脂肪酸氨基酸共轭物（FAC）[volicitin：N-(17-羟基亚麻酰基)-L-谷氨酰胺]以来，它们作为植物诱导反应激发子的作用已得到充分证明。然而，关于FAC在昆虫体内的生物合成及其生理作用的研究却很少。通过在斜纹夜蛾幼虫的饲养研究中使用（14）C标记的谷氨酰胺、谷氨酸和亚麻酸，并结合组织分析，我们发现中肠细胞中的谷氨酰胺是FAC生物合成的主要来源。此外，FAC中20%的谷氨酰胺部分是通过谷氨酰胺合成酶（GS）的酶促反应由谷氨酸和氨衍生而来。为了确定FAC是否能提高GS的生产力，我们研究了以含有（15）NH(4)Cl和谷氨酸的人工饲料喂养的斜纹夜蛾幼虫的氮同化效率。当饲料中富含亚麻酸时，氮同化效率从40%提高到了>60%。在肠腔中，生物合成的FAC被水解为脂肪酸和谷氨酰胺，它们被重新吸收到组织和血淋巴中。这些结果有力地表明，FAC在鳞翅目幼虫的氮同化中发挥着积极作用，并且肠腔中含谷氨酰胺的FAC可能作为谷氨酰胺的一种储存形式发挥作用，谷氨酰胺是氮代谢的关键化合物。
