title: Xanthosine-5'-phosphate amidotransferase from Escherichia coli.
abstract: The purified enzyme xanthosine-5'-monophosphate (XMP) aminase from Escherichia coli strain B-96 is shown to possess catalytic activity with either glutamine or ammonia as a substrate. This enzyme, which possesses identical subunits, has the following properties: (a) a pH optimum of 8.3 for both aminase and amidotransferase; (b) an apparent K-m for both glutamine and NH3 of 1 mM; (c) an amidotransferase that is approximately 2 times more active than the aminase; (d) a linear relationship between velocity and enzyme concentrationfor both activities; (e) inhibition of both activities by the glutamine analogue 6-diazo-5-oxo-L-norleucine, but the amidotransferase is more sensitive than the aminase; and (f) inhbiition of both activities by the adenosine analogue, psicofuranine, but again the amidotransferase activity is more sensitive than the aminase. The so-called XMP aminase from the E. coli mutant B-24-1 also has been examined in both crude extracts nad ammonium sulfate fractions and the following data have been obtained: (a) both preparations of enzyme contain aminase and amidotransferase activity; (b) both activities have the same substrate requirements; (c) the pH optima for both activities in the crude extract are identical with those found with the purified enzyme preparation; and (d) the amidotransferase activity in the crude extract and the ammonium sulfate fractions is 2- to 3-fold more active than the aminase. These data demonstrate that this enzyme from E. coli is not strictly a XMP aminase but is, in fact, an amidotransferase capable of utilizing either glutamine or NH3 as a substrate.
mesh_terms: D000619:Aminohydrolases / Q000378:metabolism; D000641:Ammonia / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000963:Antimetabolites / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology*; D005973:Glutamine / Q000494:pharmacology; D006150:Guanine Nucleotides; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008025:Ligases / Q000302:isolation & purification* / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D009154:Mutation; D012265:Ribonucleotides; D014970:Xanthines
chemical_list: D000900:Anti-Bacterial Agents; D000963:Antimetabolites; D006150:Guanine Nucleotides; D012265:Ribonucleotides; D014970:Xanthines; D005973:Glutamine; D000641:Ammonia; D000619:Aminohydrolases; D008025:Ligases; D008274:Magnesium; D004229:Dithiothreitol