ASL (argininosuccinate lyase) belongs to the lyase 1 family. ASL is an enzyme that catalyzes the reversible breakdown of argininosuccinate (ASA) producing the amino acids arginine and 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. While ASS (argininosuccinate synthetase) catalyzes the formation of argininosuccinate from citrulline and aspartate, ASL breaks the newly formed argininosuccinate into L-arginine and fumarate. L-arginine continues through the urea cycle to form urea and orinthine, while fumarate can enter the citric acid cycle. Recombinant human ASL protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.