In bacteria, DHOase is a dimer of identical chains of about 400 amino-acid residues. In higher eukaryotes, DHOase is part of a large multi-functional protein known as 'rudimentary' in Drosophila and CAD in mammals and which catalyzes the first three steps of pyrimidine biosynthesis. The DHOase domain is located in the central part of this polyprotein. In yeasts, DHOase is encoded by a monofunctional protein. However, a defective DHOase domain is found in a multifunctional protein that catalyzes the first two steps of pyrimidine biosynthesis.

The comparison of DHOase sequences from various sources shows that there are two highly conserved regions. The first located in the N-terminal extremity contains two histidine residues suggested to be involved in binding the zinc ion. The second is found in the C-terminal part. A signature pattern for both regions has been developed.

Alantoinase (EC 3.5.2.5) is the enzyme that hydrolyzes allantoin into allantoate. In yeast, it is the first enzyme in the allantoin degradation pathway; in amphibians and fishs it catalyzes the second step in the degradation of uric acid. The sequence of allantoinase is evolutionary related to that of DHOases.
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