Which amino acid is the most abundant in the human body?

• A. Glutamine
• B. Leucine
• C. Lysine
• D. Arginine

Answer: (A)

Glutamine is the most abundant amino acid in the human body because it serves as the main nitrogen carrier and a major fuel for several tissues, especially rapidly dividing cells like those in the gut and immune system. Muscle releases glutamine in large amounts into the bloodstream, and other tissues take it up as needed for protein synthesis, nitrogen balance, and cellular energy. It is synthesized from glutamate by glutamine synthetase, which helps maintain a large, readily available pool of glutamine in the body. While other amino acids are essential or play important roles, their free circulating pools are smaller because they’re used more rapidly for specific protein synthesis and metabolic functions, rather than serving as a large nitrogen reservoir.