ACAT1 (acetyl-Coenzyme A acetyltransferase 1) is a 417aa protein. ACAT1 is a mitochondrial enzyme involved in the formation and degradation of ketone bodies and is necessary for the proper metabolic processing of isoleucine. ACAT1 and ACAT2 catalyze the formation of acetoacetyl-CoA from two acetyl-CoA molecules. These enzymes are also capable of the reverse reaction. Defects in ACAT1 are a cause of 3-ketothiolase deficiency. 3-ketothiolase deficiency is an inborn error of isoleucine catabolism characterized by intermittent ketoacidotic attacks associated with unconsciousness. Some patients die during an attack or are mentally retarded.