Which of the following substances is a naturally occurring amino acid that acts as a precursor to carnosine?

Beta-alanine is a naturally occurring amino acid that plays a crucial role as a precursor for carnosine synthesis in the body. Carnosine, a dipeptide composed of beta-alanine and histidine, is found in high concentrations in muscle and brain tissue, where it functions primarily as a buffer against acid buildup during high-intensity exercise.

Beta-alanine itself is unique among the amino acids in that it does not appear in the genetic code as a building block for proteins. Instead, it is synthesized in the body from other amino acids and serves specifically as a substrate for the formation of carnosine. The elevation in muscle carnosine levels through supplementation with beta-alanine has been shown to enhance performance, particularly during activities that require short bursts of high-intensity effort.

The other choices, while important in their own right, do not serve this specific function. Glutamine is primarily involved in protein synthesis and immune function, L-carnitine is related to fatty acid metabolism and energy production, and leucine is a branched-chain amino acid significant for muscle protein synthesis but does not play a role in carnosine production. Therefore, beta-alanine is correctly identified as the substance that acts as a precursor to carnosine