Identification of imidazole as L-arginine-competitive inhibitor of porcine brain nitric oxide synthase.
Imidazole acts as a heme-site inhibitor of nitric oxide synthase (NOS). We used this compound to investigate whether the substrate L-arginine binds directly to the heme or to a separate domain of brain NOS. Enzyme kinetic experiments showed that imidazole enhanced the apparent Km for L-arginine without affecting maximal enzyme activity, and binding studies revealed that the inhibitor displaced the radioligand NG-nitro-L-[3H]arginine in a concentration-dependent fashion. These results demonstrate that imidazole exerts its effects on NOS in an L-arginine-competitive manner and that the substrate site of the enzyme may be identical with the prosthetic heme group.
Mayer
B
B
Institut für Pharmakologie und Toxikologie, Karl-Franzens-Universität Graz, Austria.
Klatt
P
P
Werner
E R
ER
Schmidt
K
K
D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors*; D000818:Animals; D001120:Arginine / Q000378:metabolism*; D001665:Binding Sites; D001667:Binding, Competitive; D001708:Biopterins / Q000031:analogs & derivatives / Q000378:metabolism; D001921:Brain / Q000201:enzymology; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D019001:Nitric Oxide Synthase; D013552:Swine
D007093:Imidazoles; D001708:Biopterins; C029899:imidazole; D001120:Arginine; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases; C003402:sapropterin