This study was conducted to evaluate the effects of different dipeptides (lysine-leucine, lysine-glycine, and leucine-glycine) and free amino acids (lysine and leucine) on the growth, gene expression of intestinal peptide and amino acid transporters, and serum free amino acid concentrations in turbot. Fish (11.98 ± 0.03 g) were fed four experimental diets supplementing with crystalline amino acids (CAA), lysine-leucine (Lys-Leu), lysine-glycine (Lys-Gly), and leucine-glycine (Gly-Leu). Fish protein hydrolysate (FPH) containing a mixture of free amino acids and small peptides was designed as a positive control diet. There was no significant difference in the growth and feed utilization among three dipeptide diets (Lys-Leu, Lys-Gly, and Gly-Leu). Compared with the CAA group, feed efficiency ratio was significantly higher in the Lys-Leu and Lys-Gly groups, and protein efficiency ratio was significantly higher in the Lys-Leu group. For peptide transporter, oligopeptide transporter 1 (PepT1) mRNA level was not affected by dietary treatments. For amino acid transporters, lower expression of B⁰ neutral amino acid transporter 1 (B⁰AT1) and proton-coupled amino acid transporter 1 (PAT1) were observed in fish fed the dipeptide and FPH diets compared with the CAA diet. In conclusion, juvenile turbot fed Lys-Leu, Gly-Leu, and Lys-Gly had a similar growth performance, whereas lysine and leucine in the Lys-Leu form can be utilized more efficiently for feed utilization than those in free amino acid from. In addition, compared to free amino acids, dipeptides and fish protein hydrolysate in diets may down-regulate the expression of amino acid transporters but did not affect the expression of PepT1.

本研究旨在评估不同二肽（赖氨酸-亮氨酸、赖氨酸-甘氨酸和亮氨酸-甘氨酸）和游离氨基酸（赖氨酸和亮氨酸）对生长、肠肽和氨基酸转运蛋白的基因表达以及血清的影响大菱鲆中游离氨基酸的浓度。给鱼（11.98 ± 0.03 g）喂食四种补充有结晶氨基酸（CAA）、赖氨酸-亮氨酸（Lys-Leu）、赖氨酸-甘氨酸（Lys-Gly）和亮氨酸-甘氨酸（Gly-Leu）的实验饲料。含有游离氨基酸和小肽混合物的鱼蛋白水解物（FPH）被设计为阳性对照饮食。三种二肽日粮（Lys-Leu、Lys-Gly 和 Gly-Leu）的生长和饲料利用率没有显着差异。与CAA组相比，Lys-Leu组和Lys-Gly组的饲料效率显着较高，Lys-Leu组的蛋白质效率显着较高。对于肽转运蛋白，寡肽转运蛋白 1 (PepT1) mRNA 水平不受饮食治疗的影响。对于氨基酸转运蛋白，与 CAA 饲料相比，在喂食二肽和 FPH 饲料的鱼中观察到 B ⁰中性氨基酸转运蛋白 1 (B ⁰ AT1) 和质子偶联氨基酸转运蛋白 1 (PAT1) 的表达较低。总之，饲喂 Lys-Leu、Gly-Leu 和 Lys-Gly 的幼鱼具有相似的生长性能，而 Lys-Leu 形式的赖氨酸和亮氨酸可以比游离氨基酸更有效地用于饲料利用。此外，与游离氨基酸相比，日粮中的二肽和鱼蛋白水解物可能下调氨基酸转运蛋白的表达，但不影响PepT1的表达。