What is carnosine
Carnosine is a small molecule made of two amino acids joined together. The first is beta-alanine. The second is L-histidine. The link between them is an amide bond, the same kind of bond that holds proteins together. Because it has two amino acids, it is called a dipeptide.
Identity
- Common name: L-carnosine. Chemical name: beta-alanyl-L-histidine.
- Formula: C9H14N4O3. Molar mass: 226.23 g/mol.
- CAS Registry Number: 305-84-0. PubChem CID: 439224.
- Source for these values: the Human Metabolome Database, HMDB0000033.
The two halves
Beta-alanine is not one of the 20 amino acids that build proteins. Its amino group sits one carbon further along the chain than in ordinary (alpha) alanine. On its own it has little biological activity, but the body cannot make carnosine without it. Beta-alanine supply is the step that limits how much carnosine muscle can make (Boldyrev, Aldini and Derave 2013).
L-histidine carries an imidazole ring: a five-sided ring with two nitrogen atoms. The ring is the part of carnosine that does most of the chemistry. It can take up and release hydrogen ions, bind metal ions, and react with reactive carbonyl compounds. Boldyrev, Aldini and Derave conclude that the imidazole ring is the main bioactive part of the molecule and that beta-alanine mainly controls how much of it the body makes.
The pKa and why it matters
The imidazole ring in carnosine has a pKa of 6.83 (HMDB). A buffer works best within about one pH unit of its pKa. Working muscle drops from about pH 7.1 towards pH 6.5. Carnosine’s pKa sits inside that range, so it can soak up hydrogen ions as muscle acidifies. Free histidine has a pKa near 6, which puts it at the edge of that range; joining it to beta-alanine shifts the pKa upward and makes the dipeptide a better buffer for muscle (Open Heart review, 2014).
How much of a muscle’s total buffering carnosine provides is debated. One estimate is 10 to 20 per cent (Mannion et al. 1992). A 2020 review puts it at 6 to 7 per cent at normal levels, rising to about 15 per cent after beta-alanine loading (Stellingwerff 2020, Gatorade Sports Science Institute).
Where to go next
- Names and spellings: carnosine is not carnitine.
- In food and the body: how much muscle holds, which foods contain it.
- How it works: buffering, antioxidant and metal-binding chemistry, anti-glycation.
- Carnosinase and absorption: why carnosine swallowed by a person is broken down within minutes.