- 期刊
- OpenAccess
Fatty Acid Desaturation and Stearoyl-CoA Desaturase Expression in the Hepatic Microsomes of Milkfish, Chanos chanos, under Cold Shock
虱目魚低溫下脂肪酸去飽和作用及去飽和酵素的表現
摘要
虱目魚(Chanos chanos)為台灣養殖重要經濟魚種之一，適於夏季養殖。每在冬季寒流來襲之際，因其耐寒性不足而大量凍斃至死，就虱目魚對低溫之適應，追蹤分析細胞膜脂肪酸的去飽和作用及去飽和酵素的表現。起始馴化溫度為25℃，之後再以每分鐘0.5℃的速度降溫至15℃，在不同時間點採樣分析。結果顯示，虱目魚在低溫15℃時，肝臟微粒體中的飽和脂肪酸（16: 0及18: 0）均較25℃ 時低，而單不飽和脂肪酸（16: 1及18: 1）則較25℃時高。除此之外，Δ^9去飽和指數（16: 1/16: 0及18: 1/18: 0）在低溫刺激的初期會逐漸在上升，Δ^9去飽和指數的增加，表示脂肪酸去飽和作用增加，隨後低溫刺激的後期則是緩慢的降低。在低溫環境中，stearoyl-CoA去飽和酵素跟Δ^9去飽和指數均和細胞膜上脂肪酸的去飽和作用相關，並顯示Δ^9去飽和指數表示脂肪酸去飽和作用的程度。分析虱目魚stearoyl-CoA去飽和酵素的mRNA在低溫下之表現，顯示該mRNA的確被低溫刺激所誘發，且與其酵素活性呈現平行相關變化。在相關性的分析方面，去飽和酵素，Δ^9去飽和指數以及去飽和酵素mRNA的量，在虱目魚低溫刺激下都是呈現平行相關的。這些結果證明虱目魚在低溫刺激時會增加細胞膜上脂肪酸的去飽和作用，而且脂肪酸的組成變化與脂肪酸去飽和作用呈顯著之正相關性。
並列摘要
Milkfish, a commercially important culture teleost in Taiwan, are known to be less tolerant to the cold, and the culture industry in this country has often suffered from the mass mortality of winterkills. The membrane lipid desaturation and stearoyl-CoA desaturase expression in milkfish under cold shock were investigated. Milkfish were initially acclimated at 25℃ and then exposed to cold shock of 15℃. The proportions of saturated fatty acids (16: 0 and 18: 0) in the hepatic microsomes of milkfish at 15℃ were lower, while those of monounsaturated fatty acids (16: 1 and 18: 1) were significantly higher than the control fish at 25℃. Δ^9 desaturation index gradually increased in the early period of cold shock and peaked on day 5, followed by slight decrease thereafter. Concurrent changes in Δ^9 desaturation index (16: 1/16: 0 and 18: 1/18: 0) and the proportion of fatty acids in the hepatic microsomes of milkfish were further demonstrated. The trend of stearoyl-CoA desaturase activity changes was found parallel to those of unsaturated fatty acids composition and Δ^9 desaturation index, though 1-day time lag was evident. These parameters are significantly correlated among them, and Δ^9 desaturation index can accordingly be employed to represent the degree of fatty acid desaturation, stearoyl-CoA desaturase activities and membrane fluidity as well. The expression of stearoyl-CoA desaturase mRNA in milkfish is specifically induced by a low temperature, and those in stearoyl-CoA desaturase activities were parallel to the changes in desaturase mRNA transcript. The findings suggested that the increases in the membrane lipid desaturation and stearoyl-CoA desaturase activities in milkfish under cold shock were in accordance with other teleosts being reported elsewhere, and the quantitative compensatory mechanisms are predominantly involved in the acclimation process of cold shock in this species.