Arginase is an enzyme of the urea cycle that catalyzes the following reaction:
Virtually all organisms use the reactions shown in Figure 20.13 to synthesize arginine from ornithine, but they lack the arginase enzyme needed to complete the urea cycle and thus make urea. Only ureotelic organisms-those that excrete urea-contain arginase, so only ureotelic organisms can carry out the cyclic urea cycle pathway.
See also: Urea Cycle Descriptions, Urea Cycle Reactions