Carnosine is a major constituent of
**Core Concept**
Carnosine is a dipeptide composed of the amino acids beta-alanine and histidine, playing a crucial role in buffering hydrogen ions and maintaining cellular homeostasis.
**Why the Correct Answer is Right**
Carnosine is predominantly found in muscle tissue, where it acts as a potent antioxidant, scavenging free radicals and reducing oxidative stress. Its unique structure allows it to effectively buffer hydrogen ions, thereby maintaining the pH balance within muscle cells. This property is particularly important during intense physical activity, when the accumulation of lactic acid and hydrogen ions can lead to muscle fatigue and impaired performance.
**Why Each Wrong Option is Incorrect**
**Option A:** Carnosine is not primarily associated with the nervous system, although it does have some neuromodulatory effects.
**Option B:** While carnosine does have some antioxidant properties, it is not a major constituent of the skin or hair.
**Option C:** Carnosine is not a major component of the cardiovascular system, although it may have some vasodilatory effects.
**Clinical Pearl / High-Yield Fact**
Carnosine levels in muscle tissue can be increased through supplementation with beta-alanine, which can enhance high-intensity exercise performance by delaying the onset of fatigue.
**Correct Answer:** D. Muscle tissue.