Allantoicase catalyzes the chemical reaction Thus, the two substrates of this enzyme are allantoate and H2O, whereas its two products are (S)-ureidoglycolate and urea.

Amphibians and microorganisms produce ammonia and carbon dioxide using the uricolytic pathway.

Allantoicase performs the second step in this pathway catalyzing the conversion of allantoate into ureidoglycolate and urea.

As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 1O59 and 1SG3.

The crystal structure, resolved at 2.4A resolution, reveals that AR1 has a very similar fold to AR2, both repeats being jelly-roll motifs, composed of four-stranded and five-stranded antiparallel beta-sheets.