Glutamine precursor supplementation increases glutamine synthetase gene expression in intestine of common carp (Cyprinus carpio)

To evaluate if the addition of glutamine (Gln) precursors could enhance the utilization rate of plant protein on molecular level, the expressions of glutamine synthetase (GS) gene were analysed under supplementation of a-ketoglutaric acid (AKG), ornithine-a-ketoglutaric acid (OKG), glutamic acid (Glu), and Gln. The relative quantification of GS gene expression in the plant meal (PM) group was significantly lower than the fish meal (FM) group. All the four additives increased the GS gene expression. The additive that most significantly increased the GS gene expression, Gln concentration and GS activity was glutamic acid. Supplementation of AKG in plant meal can improve the GS activity and Gln concentration. Effect of OKG on the activity of GS was not significant. The GS expression was up-regulated by Gln, but had no significant effects on the Gln concentration and GS activity. In conclusion, substitution of plant protein for animal protein reduced the GS gene expression, and the supplementation of Gln precursors was capable of promoting the expression of GS gene in common carp.