Dihydroorotase: An enzyme that, in the course of pyrimidine biosynthesis, catalyzes ring closure by removal of water from N-carbamoylaspartate to yield dihydro-orotic acid. EC 3.5.2.3.Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing): An enzyme that catalyzes the formation of carbamoyl phosphate from ATP, carbon dioxide, and glutamine. This enzyme is important in the de novo biosynthesis of pyrimidines. EC 6.3.5.5.Aspartate Carbamoyltransferase: An enzyme that catalyzes the conversion of carbamoyl phosphate and L-aspartate to yield orthophosphate and N-carbamoyl-L-aspartate. (From Enzyme Nomenclature, 1992) EC 2.1.3.2.Dihydroorotate Oxidase: An enzyme that in the course of pyrimidine biosynthesis, catalyzes the oxidation of dihydro-orotic acid to orotic acid utilizing oxygen as the electron acceptor. This enzyme is a flavoprotein which contains both FLAVIN-ADENINE DINUCLEOTIDE and FLAVIN MONONUCLEOTIDE as well as iron-sulfur centers. EC 1.3.3.1.Orotic AcidAmidohydrolasesPyrimidine Nucleotides: Pyrimidines with a RIBOSE and phosphate attached that can polymerize to form DNA and RNA.Orotate Phosphoribosyltransferase: The enzyme catalyzing the formation of orotidine-5'-phosphoric acid (orotidylic acid) from orotic acid and 5-phosphoribosyl-1-pyrophosphate in the course of pyrimidine nucleotide biosynthesis. EC 2.4.2.10.Multienzyme Complexes: Systems of enzymes which function sequentially by catalyzing consecutive reactions linked by common metabolic intermediates. They may involve simply a transfer of water molecules or hydrogen atoms and may be associated with large supramolecular structures such as MITOCHONDRIA or RIBOSOMES.Razoxane: An antimitotic agent with immunosuppressive properties.Orotidine-5'-Phosphate Decarboxylase: Orotidine-5'-phosphate carboxy-lyase. Catalyzes the decarboxylation of orotidylic acid to yield uridylic acid in the final step of the pyrimidine nucleotide biosynthesis pathway. EC 4.1.1.23.Carbamoyl-Phosphate Synthase (Ammonia): An enzyme that catalyzes the formation of carbamoyl phosphate from ATP, carbon dioxide, and ammonia. This enzyme is specific for arginine biosynthesis or the urea cycle. Absence or lack of this enzyme may cause CARBAMOYL-PHOSPHATE SYNTHASE I DEFICIENCY DISEASE. EC 6.3.4.16.Cobalt: A trace element that is a component of vitamin B12. It has the atomic symbol Co, atomic number 27, and atomic weight 58.93. It is used in nuclear weapons, alloys, and pigments. Deficiency in animals leads to anemia; its excess in humans can lead to erythrocytosis.Pyrimidines: A family of 6-membered heterocyclic compounds occurring in nature in a wide variety of forms. They include several nucleic acid constituents (CYTOSINE; THYMINE; and URACIL) and form the basic structure of the barbiturates.Phosphonoacetic Acid: A simple organophosphorus compound that inhibits DNA polymerase, especially in viruses and is used as an antiviral agent.Mesocricetus: A genus of the family Muridae having three species. The present domesticated strains were developed from individuals brought from Syria. They are widely used in biomedical research.Carcinoma, Ehrlich Tumor: A transplantable, poorly differentiated malignant tumor which appeared originally as a spontaneous breast carcinoma in a mouse. It grows in both solid and ascitic forms.Zinc: A metallic element of atomic number 30 and atomic weight 65.38. It is a necessary trace element in the diet, forming an essential part of many enzymes, and playing an important role in protein synthesis and in cell division. Zinc deficiency is associated with ANEMIA, short stature, HYPOGONADISM, impaired WOUND HEALING, and geophagia. It is known by the symbol Zn.Escherichia coli: A species of gram-negative, facultatively anaerobic, rod-shaped bacteria (GRAM-NEGATIVE FACULTATIVELY ANAEROBIC RODS) commonly found in the lower part of the intestine of warm-blooded animals. It is usually nonpathogenic, but some strains are known to produce DIARRHEA and pyogenic infections. Pathogenic strains (virotypes) are classified by their specific pathogenic mechanisms such as toxins (ENTEROTOXIGENIC ESCHERICHIA COLI), etc.