Abstract

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.