Beta-alanine combines with ________ to increase muscle carnosine stores.

Beta-alanine combines with histidine to increase muscle carnosine stores. Carnosine is a dipeptide composed of beta-alanine and histidine, and it plays a critical role in muscle function by acting as a buffer to reduce acidity in muscles during intense exercise.

When beta-alanine is ingested, it increases the levels of beta-alanine in the body, which subsequently enhances the synthesis of carnosine when it combines with histidine. This process is particularly beneficial for athletes and individuals engaged in high-intensity workouts, as higher muscle carnosine levels can lead to improved performance and reduced muscle fatigue.

Understanding the function of histidine in this context is key, as it is an essential amino acid that contributes to the formation of carnosine and is not directly supplied by beta-alanine. The other amino acids listed—valine, lysine, and phenylalanine—do not play a role in the synthesis of carnosine and therefore are not relevant in this process.