Glutamine is the most abundant free amino acid circulating in the blood as well as stored in the skeletal muscles. Glutamine is a diverse amino acid that is utilized in numerous vital functions. It is necessary for rapidly dividing cells, including those of the gut and immune system.It is also used as an energy source in mitochondria, and is a precursor of the brain neurotransmitter glutamate.Glutamine is also needed for optimal nucleotide biosynthesis and protein synthesis.