Succinimide and glutarimide, and sulfur-containing cyclic imides, such as rhodanine, can also act as substrates for the enzyme from Blastobacter sp. A17p-4. The reverse, cyclization, reaction is also catalysed, but much more slowly. It has lower activity towards cyclic ureides, which are the substrates of EC 3.5.2.2, dihydropyrimidinase.