CIMAR/CIIMAR-Centro Interdisciplinar de Investigação Marinha e Ambiental, and ICBAS-Instituto de Ciências Biomédicas de Abel Salazar, Universidade do Porto, Rua dos Bragas, 289, 4050-123, Porto, Portugal.
Amino Acids. 2010 Nov;39(5):1401-16. doi: 10.1007/s00726-010-0599-y. Epub 2010 May 5.
The objective of the present work is to investigate the main metabolic pathways by which dispensable amino acids (DAA) are diverted towards lipid formation in blackspot seabream. For that purpose, a control diet was formulated to contain 45% of crude protein (7.2 g N/100 g dry matter) mainly supplied by fish meal (45P). In two other diets, 22.2% of the dietary nitrogen (1.6 g N/100 g dry matter) was replaced by an equivalent amount of nitrogen provided by two different mixtures of DAA: alanine and serine (diet AS) or aspartic and glutamic acid (diet AG). A fourth diet (diet 35P) only containing 35% of crude protein (5.6 g N/100 g dry matter) was included in order to analyze the possible additive effects of DAA. Compared to fish fed diet 35P, blackspot seabream appear to make a more efficient use of the nitrogen provided by alanine and serine than that provided by aspartic and glutamic acids in terms of growth. Contrary to fish fed AG, fish fed AS attained similar specific FAS activities as 45P fed fish, suggesting a further role of alanine and serine on this lipogenic pathway. Dietary nitrogen reduction (45P vs. 35P) or its replacement by a mixture of aspartic and glutamic acids (diet AG) were shown to up-regulate phosphoenolpyruvate carboxykinase (PEPCK) but without, however, any effect on plasma glucose levels. Dietary nitrogen level and nature seems to exert a complex regulation on energetic pathways through the gluconeogenesis/tricarboxylic acids cycle interaction.
本研究旨在探讨黑鲷鱼体中必需氨基酸（DAA）向脂类合成途径转变的主要代谢途径。为此，配制了一种对照饲料，粗蛋白含量为 45%（7.2 g N/100 g 干物质），主要由鱼粉（45P）提供。在另外两种饲料中，用两种不同的 DAA 混合物（丙氨酸和丝氨酸（AS 饲料）或天冬氨酸和谷氨酸（AG 饲料））等量替代饲料中的 22.2%的饲料氮（1.6 g N/100 g 干物质）。为了分析 DAA 的可能的附加作用，还包含了一种仅含 35%粗蛋白（5.6 g N/100 g 干物质）的饲料（35P 饲料）。与饲喂 35P 饲料的黑鲷鱼相比，在生长方面，黑鲷鱼似乎更有效地利用了丙氨酸和丝氨酸提供的氮，而不是天冬氨酸和谷氨酸提供的氮。与饲喂 AG 的黑鲷鱼不同，饲喂 AS 的黑鲷鱼获得了与饲喂 45P 饲料的黑鲷鱼相似的特异性 FAS 活性，这表明丙氨酸和丝氨酸在该脂生成途径中可能发挥了进一步的作用。与 45P 饲料相比，降低饲料氮（45P 饲料与 35P 饲料）或用天冬氨酸和谷氨酸混合物替代（AG 饲料）会导致磷酸烯醇丙酮酸羧激酶（PEPCK）上调，但不会对血浆葡萄糖水平产生任何影响。然而，饲料氮水平和氮源似乎通过糖异生/三羧酸循环相互作用对能量途径产生了复杂的调节作用。
