Arylamine N-acetyltransferase (NAT) is a cytosolic enzyme of approximately 30kDa. It facilitates the transfer of an acetyl group from Acetyl Coenzyme A on to a wide range of arylamine, N-hydroxyarylamines and hydrazines. Acetylation of these compounds generally results in inactivation. NAT is found in many species from Mycobacteria (M. tuberculosis, M. smegmatis etc) to man. It was the first enzyme to be observed to have polymorphic activity amongst human individuals. NAT is responsible for the inactivation of Isoniazid (a drug used to treat Tuberculosis) in humans. The NAT protein has also been shown to be involved in the breakdown of folic acid.