L-citrulline production from L-arginine by macrophage nitric oxide synthase. The ureido oxygen derives from dioxygen

J Biol Chem. 1990 Aug 15;265(23):13442-5.


Previously proposed mechanisms for the production of L-citrulline from L-arginine by macrophage nitric oxide (NO.) synthase involve either hydrolysis of arginine or hydration of an intermediate and thus predict incorporation of water oxygen into L-citrulline. Macrophage NO. synthase was incubated with L-arginine, NADPH, tetrahydrobiopterin, FAD, and dithiothreitol in H2(18)/16O2. L-Citrulline produced in this reaction was analyzed with gas chromatography/mass spectrometry. Its mass spectrum matched that of L-citrulline generated in H2(16)O/16O2. The base fragment ion of m/z 99 was shown to contain the ureido carbonyl group by using L-[guanidino-13C]arginine as substrate. When the enzyme reaction was performed in H2(16)O/18O2, the base fragment ion shifted to m/z 101 with L-[guanidino-12C]arginine as the substrate and to m/z 102 with L-[guanidino-13C]arginine. These results indicate that the ureido oxygen of the L-citrulline product of macrophage NO.synthase derives from dioxygen and not from water.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Oxidoreductases / metabolism*
  • Animals
  • Arginine / metabolism*
  • Cell Line
  • Citrulline / biosynthesis*
  • Cytosol / metabolism
  • Gas Chromatography-Mass Spectrometry
  • Interferon-gamma / pharmacology
  • Lipopolysaccharides / pharmacology
  • Macrophages / drug effects
  • Macrophages / enzymology*
  • Mass Spectrometry
  • Nitric Oxide Synthase
  • Oxygen / metabolism*
  • Oxygen Isotopes


  • Lipopolysaccharides
  • Oxygen Isotopes
  • Citrulline
  • Interferon-gamma
  • Arginine
  • Nitric Oxide Synthase
  • Amino Acid Oxidoreductases
  • Oxygen