title: The mammalian enzyme which replaces B protein of E. coli quinolinate synthetase is D-aspartate oxidase.
abstract: In Escherichia coli quinolinic acid, a precursor of NAD+, is synthesized from L-aspartate and dihydroxyacetone phosphate by two enzymes, an FAD-containing 'B protein' and 'A protein'. An enzyme which can replace the B protein in the E. coli quinolinate synthetase system when D-aspartate replaces L-aspartate as a substrate has been purified 300-fold from bovine kidney. This enzyme is shown to be identical with the previously described D-aspartate oxidase (D-aspartate:oxygen oxidoreductase (deaminating), EC 1.4.3.1). The immediate reaction product of D-aspartate oxidase (iminoaspartate) is condensed with dihydroxyacetone phosphate to form quinolinate in a reaction catalyzed by E. coli quinolinate synthetase A protein. In the absence of A protein (or dihydroxyacetone phosphate) iminoaspartate is spontaneously hydrolyzed to form oxaloacetate with a half-life of about 2.5 min at 25 degrees C and pH 8.0.
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D050804:D-Aspartate Oxidase; D004926:Escherichia coli / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D046911:Macromolecular Substances; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000378:metabolism*; D051381:Rats; D013696:Temperature
chemical_list: D046911:Macromolecular Substances; D009097:Multienzyme Complexes; C022512:quinolinic acid synthetase; D000594:Amino Acid Oxidoreductases; D050804:D-Aspartate Oxidase