title: Imidase, a dihydropyrimidinase-like enzyme involved in the metabolism of cyclic imides.
abstract: Imidase, which preferably hydrolyzed cyclic imides to monoamidated dicarboxylates, was purified to homogeneity from a cell-free extract of Blastobacter sp. A17p-4. Cyclic imides are known to be hydrolyzed by mammalian dihydropyrimidinases. However, imidase was quite different from known dihydropyrimidinases in structure and substrate specificity. The enzyme has a relative molecular mass of 105 000 and consists of three identical subunits. The purified enzyme showed higher activity and affinity toward cyclic imides, such as succinimide (Km = 0.94 mM; Vmax = 910 micromol x min(-1) x mg(-1)), glutarimide (Km = 4.5 mM; Vmax = 1000 micromol min (-1) x mg (-1) and maleimide (Km = 0.34 mM; Vmax = 5800 micromol x min(-1)x mg(-1)), than toward cyclic ureides, which are the substrates of dihydropyrimidinases, such as dihydrouracil and hydantoin. Sulfur-containing cyclic imides, such as 2,4-thiazolidinedione and rhodanine, were also hydrolyzed. The enzyme catalyzed the reverse reaction, cyclization, but with much lower activity and affinity. The enzyme was non-competitively inhibited by succinate, which was found to be a key compound in cyclic-imide transformation in relation with the tricarboxylic acid cycle in this bacterium, suggesting that the role of imidase is to catalyze the initial step of cyclic-imide degradation.
authors.affiliation: Department of Agricultural Chemistry, Kyoto University, Sakyo-ku, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Ogawa
authors.forename: C L
authors.initials: CL
authors.lastname: Soong
authors.forename: M
authors.initials: M
authors.lastname: Honda
authors.forename: S
authors.initials: S
authors.lastname: Shimizu
mesh_terms: D000581:Amidohydrolases / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D000595:Amino Acid Sequence; D001419:Bacteria / Q000201:enzymology*; D001426:Bacterial Proteins / Q000302:isolation & purification; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007094:Imides / Q000378:metabolism*; D007700:Kinetics; D008670:Metals / Q000494:pharmacology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D012988:Soil Microbiology; D013379:Substrate Specificity; D013388:Succinimides / Q000378:metabolism; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D007094:Imides; D008670:Metals; D013388:Succinimides; C032620:succinimide; D000581:Amidohydrolases; C020047:dihydropyrimidinase