ASL (argininosuccinatelyase, also known as argininosuccinase) is an enzyme that catalyzes the reversible breakdown of argininosuccinate (ASA) producing the amino acid arginine and dicarboxylic acid fumarate. Located in liver cytosol, ASL is the fourth enzyme of the urea cycle and involved in the biosynthesis of arginine in all species and the production of urea in ureotelic species. Mutations in ASL, resulting low activity of the enzyme, increase levels of urea in the body and result in various side effects. The ASL gene is located on chromosome 7 between the centromere (junction of the long and short arm) and the long (q) arm at position 11.2, from base pair 64,984,963 to base pair 65,002,090.