Carnosine, which is also known as beta-alanyl-L-histidine) is a dipeptide consisting of the amino acids beta-alanine and histidine. It is found exclusively in animal tissues and is naturally produced in the body by the liver. Carnosine has a pKa value of 6.83, making it a good buffer for the pH range of animal muscles.  Since beta-alanine is a non-proteogenic amino acid and is not incorporated into proteins, carnosine can be stored at relatively high concentrations (millimolar) in muscles, with concentrations as high as 17‚Äì25 mmol/kg (dry muscle). Carnosine is also highly concentrated in brain tissues. Carnosine has been shown to scavenge reactive oxygen species (ROS) as well as alpha-beta unsaturated aldehydes formed from peroxidation of fatty acids during oxidative stress. The antioxidant mechanism of carnosine is attributed to its chelating effect against divalent metal ions, superoxide dismutase (SOD)-like activity, as well as its ROS and free radicals scavenging ability (PMID: 16406688). Carnosine also buffers muscle cells, and acts as a neurotransmitter in the brain. Carnosine has the potential to suppress many of the biochemical changes that accompany ageing (e.g. protein oxidation, glycation, AGE formation, and cross-linking) and associated pathologies (PMID: 16804013). Some autistic patients take carnosine as a dietary supplement and attribute an improvement in their condition to it. Supplemental carnosine may increase corticosterone levels. This may explain the "hyperactivity" seen in autistic subjects at higher doses. A positive association between muscle tissue carnosine concentration and exercise performance has been found. Œ≤-Alanine supplementation is thought increase exercise performance by promoting carnosine production in muscle. Exercise has conversely been found to increase muscle carnosine concentrations, and muscle carnosine content is higher in athletes engaging in anaerobic exercise. Carnosine is also a biomarker for the consumption of meat. Elevated levels of urinary and plasma carnosine are associated with carnosinuria (also known as carnosinemia), which is an inborn error of metabolism. caused by a deficiency of the enzyme carnosinase. Carnosinas cleaves carnosine into its constituent amino acids: Œ≤-Alanine and histidine. Carnonsinemia results in an excess of carnosine in the urine, cerebrospinal fluid, blood, and nervous tissue. A variety of neurological symptoms have been associated with carnosinemia. They include: hypotonia, developmental delay, mental retardation, degeneration of axons, sensory neuropathy, tremors, demyelinization, gray matter anomalies, myoclonic seizures, and loss of purkinje fibers.