Glutamine is the most abundant free amino acid within the human muscle and blood. It can be found circulating in the blood, as well as stored in the skeletal muscles and liver, in concentrations ranging from 10-100x higher than any other amino acid. 

Glutamine is a building block for protein and involved in many vital functions. It is required for rapidly dividing cells, including those of the gut, and is a precursor of the brain neurotransmitter glutamate.

Certain factors such as heavy exercising can lower the glutamine levels in the body. Glutamine supplements cause a rapid rise in cellular glutamine levels and glutamine stores in muscle.