Stable isotope analysis by fast-atom bombardment labeling of UDP-glucuronic acid

Fast-atom bombardment mass spectrometry is found to provide a method for analysis of isotopes in the enzyme cofactor uridine-5'-diphosphoglucuronic acid, heretofore unsusceptible to mass-spectral characterization. This technique was used to determine optimal conditions for the introduction of 18O by acid-catalyzed exchange in H218O and to evaluate the loss of the isotope when labeled cofactor is used in enzymatic incubations. Fast-atom bombardment mass spectrometry provided a quantitative assessment of various isotopic species and also permitted the location of the isotopes in the molecule to be determined.