Catalyzes the transfer of the acetyl group from acetyl coenzyme A to the free amino group of arylamines and hydrazines (PubMed:18795795). Is able to utilize not only acetyl-CoA, but also n-propionyl-CoA and acetoacetyl-CoA as acyl donors, although at a lower rate (PubMed:19014350). As acetyl-CoA and propionyl-CoA are products of cholesterol catabolism and the nat gene is likely present in the same operon than genes involved in cholesterol degradation, this enzyme could have a role in the utilization and regulation of these CoA species (PubMed:19014350). It has been reported that overexpression of this enzyme may be responsible for increased resistance to the front-line antitubercular drug isoniazid (INH), by acetylating and hence inactivating the prodrug (PubMed:9973365). However, isoniazid is an extremely poor substrate for the enzyme; therefore, the expression of TBNAT is unlikely to be a significant cause of isoniazid resistance in M.tuberculosis (PubMed:18795795). acetyl-CoA + an arylamine = an N-acetylarylamine + CoA kcat is 94 sec(-1) with 3-amino-4-hydroxybenzoic acid as substrate. kcat is 66 sec(-1) with 4-amino-3-hydroxybenzoic acid as substrate. kcat is 44 sec(-1) with hydralazine as substrate. kcat is 70 sec(-1) with 2-amino-4-methylphenol as substrate. kcat is 21 sec(-1) with 2-amino-4-chlorophenol as substrate. kcat is 51 sec(-1) with 2-aminophenol as substrate. kcat is 10.9 sec(-1) with 4-hydroxybenzhydrazide as substrate. kcat is 2.9 sec(-1) with anisidine as substrate. kcat is 0.7 sec(-1) with p-aminobenzoic acid as substrate. kcat is 1.9 sec(-1) with benzoic acid hydrazide as substrate. kcat is 0.8 sec(-1) with 4-methylaniline as substrate. kcat is 4.9 sec(-1) with isoniazid as substrate. kcat is 0.6 sec(-1) with nicotinic acid hydrazide as substrate. kcat is 0.2 sec(-1) with 4-chloroaniline as substrate. kcat is 0.28 sec(-1) with aniline as substrate. kcat is 0.9 sec(-1) with 4-fluoroaniline as substrate. Is thermostable. Retains >95% of its activity after incubation at 60 degrees Celsius for 30 minutes. Homodimer and homotetramer. Was identified as a high-confidence drug target. Reactions proceed via a bi-bi ping-pong kinetic mechanism. Resistance to the antitubercular drug isoniazid (INH) has been associated to mutations in this gene in some INH-resistant clinical isolates of M.tuberculosis. Belongs to the arylamine N-acetyltransferase family.