The effect of dietary dipeptide lysine–glycine on growth, muscle proteins, and intestine PepT1 gene expression in juvenile yellow perch

The objective of the present study was to examine the effect of a wheat-gluten-based diet supplemented with the indispensable amino acid source in the form of free amino acid or dipeptide on growth, intestine oligopeptide transporter, PepT1, transcript levels using real-time RT-PCR, and muscle protein expression in yellow perch Perca flavescens juveniles. Yellow perch (initial size ~0.3 g) were randomly distributed into 12 glass aquaria, 60 fish per tank. Fish were fed 4 diets: wheat-gluten based diet supplemented with lysine–glycine dipeptide (LG), wheat-gluten based diet supplemented with free lysine (FL), diet not supplemented with lysine (NL; negative control) and a commercial diet (BO). Fish were fed at 90 % satiation level and the rate was re-adjusted to be equal across all treatments based on each day’s projected change in weight gain. It amounted to 3 % of the biomass per day for the first 14 days and 4–5 % until the end of the experiment. After 55 days of the experiment the mean weight of juvenile yellow perch fed the LG diet was larger compared to the NL diet fed group. There was no difference, however, between LG, FL, and BO groups (1.35 ± 0.11 g; 1.31 ± 0.03; 1.16 ± 0.10 g, respectively). Fish subjected to FL treatment showed an increase in the amount of PepT1 transcripts compared to the NL group value. The LG diet was associated with a significant increase in PepT1 mRNA transcript levels, compared with both FL and NL diets fed fish. We have also cloned and sequenced full-length cDNA representing yellow perch PepT1. The cDNA sequence (GeneBank: accession no. GQ906471), encompasses a total of 2,956 base pairs (bp) including a 5′-untranslated region of 94 bp, an open reading frame of 2,190 bp, and a 3′-untranslated region of 672 bp. The predicted 12 transmembrane domains and the 3D structure of the protein (729 amino acids) are presented. Proteomic fingerprinting showed that thirteen electrophoretically resolved protein/peptide bands from the muscle sarcoplasmic fraction were significantly different across treatments suggesting that muscle protein expression was influenced by dietary treatments.