The effect of the dipeptide, Lys-Gly, supplement on growth, muscle proteins and 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 freeamino 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 (Gene-
Bank: accession no.GQ906471), encompasses a total of
2,956 base pairs (bp) including a 50-untranslated region
of 94 bp, an open reading frame of 2,190 bp, and a 30-
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.