Nitric oxide synthase from cerebellum catalyzes the formation of equimolar quantities of nitric oxide and citrulline from L-arginine

Biochem Biophys Res Commun. 1992 Jun 30;185(3):960-6. doi: 10.1016/0006-291x(92)91720-b.


This study examined whether constitutive nitric oxide (NO) synthase from rat cerebellum catalyzes the formation of equimolar amounts of NO plus citrulline from L-arginine under various conditions. Citrulline was determined by monitoring the formation of 3H-citrulline from 3H-L-arginine. NO was determined by monitoring the formation of total NOx (NO+nitrite [NO2-] + nitrate [NO3-]) by chemiluminescence after reduction of NOx to NO by acidic vanadium (III). Equal quantities of NO plus citrulline were generated from L-arginine and the formation of both products was linear for about 20 min at 37 degrees C provided L-arginine was present in excess to maintain a zero order reaction rate. Deletion of NADPH, addition of the calmodulin antagonist calmidazolium, or addition of NO synthase inhibitors (NG-methyl-L-arginine, NG-amino-L-arginine) abolished or markedly inhibited the formation of both NO and citrulline. The Km for L-arginine (14 microM; 18 microM) and the Vmax of the reaction (0.74 nmol/min/mg protein; 0.67 nmol/min/mg protein) were the same whether NO or citrulline formation, respectively, was monitored. These observations indicate clearly that NO and citrulline are formed in equimolar quantities from L-arginine by the constitutive isoform of NO synthase from rat cerebellum.

Publication types

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

MeSH terms

  • Amino Acid Oxidoreductases / isolation & purification
  • Amino Acid Oxidoreductases / metabolism*
  • Animals
  • Arginine / metabolism*
  • Cerebellum / enzymology*
  • Citrulline / metabolism*
  • Kinetics
  • Luminescent Measurements
  • Male
  • Nitric Oxide / metabolism*
  • Nitric Oxide Synthase
  • Radioisotope Dilution Technique
  • Rats
  • Rats, Inbred Strains
  • Tritium


  • Tritium
  • Citrulline
  • Nitric Oxide
  • Arginine
  • Nitric Oxide Synthase
  • Amino Acid Oxidoreductases