title: Biosynthesis of nitric oxide and citrulline from L-arginine by constitutive nitric oxide synthase present in rabbit corpus cavernosum.
abstract: The objective of this study was to determine whether a constitutive isoform of nitric oxide (NO) synthase is present in rabbit corpus cavernosum that could account for the involvement of the L-arginine-NO pathway in neurogenically-elicited relaxation of the corpus cavernosum and, therefore, penile erection. Citrulline was determined by monitoring the formation of 3H-citrulline from 3H-L-arginine. NO was determined by monitoring the formation of total NO(x) (NO+nitrite [NO2-]+nitrate [NO3-]) by chemiluminescence after reduction of NO(x) to NO by acidic vanadium (III). Equimolar quantities of NO plus citrulline were generated from L-arginine and the formation of both products was time-dependent at 37 degrees C. NO synthase activity was distributed almost entirely to the cytosolic fraction. Enzymatic activity was completely dependent on NADPH, calmodulin, and calcium. Addition of tetrahydrobiopterin increased NO synthase activity by about 30 percent. The NO synthase inhibitor NG-nitro-L-arginine, abolished enzymatic activity. The Km for L-arginine was 17 microM and the Vmax of the reaction was 18 pmol/min/mg protein. These observations indicate that a cytosolic, constitutive isoform of NO synthase, like that found in brain neuronal tissue, is present in rabbit corpus cavernosum.
authors.affiliation: Department of Pharmacology, UCLA School of Medicine 90024.
authors.forename: P A
authors.initials: PA
authors.lastname: Bush
authors.forename: N E
authors.initials: NE
authors.lastname: Gonzalez
authors.forename: L J
authors.initials: LJ
authors.lastname: Ignarro
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000378:metabolism*; D000818:Animals; D001120:Arginine / Q000378:metabolism*; D002956:Citrulline / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase; D010413:Penis / Q000201:enzymology*; D011817:Rabbits; D013347:Subcellular Fractions / Q000201:enzymology
chemical_list: D002956:Citrulline; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases