ABSTRACT
Glutamine is a nonessential amino acid (NEAA) but becomes a conditionally essential amino acid in catabolic states because of the body’s inability to synthesize sufficient amounts of glutamine during stress. The enzyme glutaminase catalyzes the hydrolysis of glutamine to glutamate while glutamine synthetase (GS) catalyzes the synthesis of glutamine from glutamate and ammonia. The liver possesses both enzymes because it can switch from net glutamine utilization to net production, depending on physiological and nutritional conditions. Glutamine is the most abundant free amino acid in the body and is nutritionally classified among the NEAA such as glutamate, proline, glycine, and arginine. Glutamine has been shown to regulate the expression of many genes related to metabolism to activate several proteins. Glutamine was added to drinking water for 7 consecutive days each month after 5-day fasting to determine whether GS enhancement induced by fasting disappeared with glutamine supply irrespective of the age of the animal.
