The Biochemistry of Argininosuccinate Lyase Deficiency Part I: The Urea Cycle

The Urea cycle, as mentioned before, is a series of chemical reactions which aid in the removal of ammonia from the body. In the process, it produces two amino acid called arginine and ornithine. Both are important to the body in their own ways, and patients of ASLD have to find alternate ways to introduce these into their systems.

Besides producing amino acids, the urea cycle serves to remove nitrogenous metabolic wastes from the body mainly in the form of ammonia mostly by converting it to urea which can then be excreted. As can be seen from the diagram above, reaction 4 involves argininosuccinate being converted to Fumarate and L-Arginine. The enzyme which catalyses this reaction is argininosuccinate lyase. Without this enzyme, the metabolic products from previous reactions build up. Imagine a traffic jam, where argininosuccinate lyase has gotten into an accident, blocking up the road. Eventually, all the preceding products will build up to dangerous levels, ending finally in hyperammonmemia

In a nutshell, the Urea Cycle is a series of processes which convert nitrogenous metabolic wastes, mostly in the form of ammonia, into Urea for removal from the body system, while synthesizing necessary amino acids such as Arginine and Ornithine needed for different processes in the body.

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