Dihydropyrimidinase. Metabolism of some cyclic imides of different ring size.

The ability of dihydropyrimidinase (EC 3.5.2.2) to hydrolyze cyclic imides of different ring size was investigated. Succinimide, glutarimide, and adipimide are five-, six-, and seven-membered cyclic imides, respectively. The ring-opened compounds that correspond to these cyclic imides are, respectively, succinamic, glutaramic, and adipamic acid. In incubations of cyclic imides (pH 8, 1 hr) with a rat liver dihydropyrimidinase preparation from which omega-amidase had been removed, adipimide was classed as a good substrate and succinimide and glutarimide were classed as very poor but definite substrates. alpha-Phenylsuccinimide, the N-demethylated metabolite of phensuximide, was a much better substrate than succinimide. alpha-Phenylglutarimide was not a substrate. The in vitro studies of the present investigation were in agreement with observations made in previous in vivo studies.