Acyl-CoA thioesterases (ACOTs) are a group of enzymes that catalyze the hydrolysis of acyl-CoA to form coenzyme A (CoA) and a free fatty acid. Through their catalytic activity, ACOTs are able to regulate the level of fatty acids and acyl-CoAs within the cell. ACOT9 (acyl-CoA thioesterase 9), also known as ACATE2, MT-ACT48 (mitochondrial acyl-CoA thioesterase of 48 kDa) or CGI-16, is a 406 amino acid member of the acyl-CoA hydrolase protein family. ACOT9 contains a C-terminal 80-amino acid domain that is conserved from mouse to human, suggesting that the C-terminus may confer the catalytic activity of ACOT9. The gene encoding ACOT9 is located on chromosome X and the expressed ACOT9 protein is localized to the mitochondrion.