Effects of lysine and leucine in free and different dipeptide forms on the growth, amino acid profile and transcription
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Effects of lysine and leucine in free and different dipeptide forms on the growth, amino acid profile and transcription of intestinal peptide, and amino acid transporters in turbot (Scophthalmus maximus) Yuliang Wei Liang
& Benxiang Li & Houguo Xu & Mengqing
Received: 7 August 2019 / Accepted: 26 May 2020 # Springer Nature B.V. 2020
Abstract This study was conducted to evaluate the effects of different dipeptides (lysine-leucine, lysineglycine, 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 Y. Wei : B. Li : H. Xu : M. Liang Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, 106 Nanjing Road, Qingdao 266071, China Y. Wei : H. Xu : M. Liang (*) Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, 1 Wenhai Road, Qingdao 266237 Shandong, China e-mail: [email protected]
diet. In conclusion, juvenile turbot fed Lys-Leu, GlyLeu, 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. Keywords Turbot . Dipeptide . Lysine . Leucine . Amino acid transporter . Peptide transporter
Introduction Fish from aquaculture are important sources of animal protein for millions of people. Global aquaculture has remained at an annual growth rate of 5.8% during the period 2000–2016, which has become one of the fastestgrowing major food production sectors in the world. Fish meal in aquafeeds is the major protein source for carnivorous fish. However, fish meal production has followed a fluctuating but overall declining trend since 1994 (FAO 2018). If aquaculture maintains a steady growth over the next few years, f
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