GNC Pro Performance L-Glutamine 5000 mg GNC Pro Performance L-Glutamine is a key amino acid for muscles*. Supplementation may help maintain glutamine levels that have been depleted as a result of intense exercise.* Glutamine is involved in protein synthesis and plays a pivotal role in the body's nitrogen balance.*ˆ It serves as a fuel for the immune system and maintenance of proper intestinal function.*  Tested and certified Banned Substance Free♦ Gluten and lactose free Mixes easily with your favorite beverage. ˆWhen used in conjunction with an exercise program.