Acetyl-CoA is an essential cofactor and carrier of acyl groups in enzymatic acetyl transfer reactions. It is formed either by the oxidative decarboxylation of pyruvate in mitochondria, by the oxidation of long-chain fatty acids, or by the oxidative degradation of certain amino acids. It is a key precursor in lipid biosynthesis, and the source of all fatty acid carbons. It is a positive regulator of pyruvate carboxylase. It is a precursor of the neurotransmitter acetylcholine.