Nitric oxide synthase in cat brain: cofactors--enzyme-substrate interaction.
Nitric oxide, derived from L-arginine by the enzyme nitric oxide synthase, is an activator of the soluble guanylate cyclase and a cellular messenger. This work demonstrates that, in cat brain, the neuronal constitutive nitric oxide synthase activity is a) NADPH/calcium dependent, b) independent upon exogenous calmodulin in crude brain supernatant, c) significantly enhanced by exogenous FAD and tetrahydrobiopterin (Vmax: 118 instead of 59.4 pmol of citrulline formed .mg of prot.-1 min-1, d) inhibited by calcium chelators and calmodulin antagonist, and e) present in several neuroanatomical structures. Moreover, the Km value for L-arginine was of 11 microM instead of 41 microM in the presence of FAD and tetrahydrobiopterin in the incubation mixture, thus demonstrating that these cofactors are able to stabilize the enzyme-substrate interactions.
Côté
J F
JF
INRS-Santé, Université du Québec, Pointe-Claire, Canada.
Roberge
A G
AG
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001921:Brain / Q000201:enzymology*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002415:Cats; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D007700:Kinetics; D008297:Male; D009249:NADP / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009928:Organ Specificity; D013449:Sulfonamides / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology; D019323:omega-N-Methylarginine / Q000494:pharmacology
D013449:Sulfonamides; D014665:Vasodilator Agents; D019323:omega-N-Methylarginine; D004533:Egtazic Acid; D009249:NADP; C017967:W 7; D001120:Arginine; D004492:Edetic Acid; D019001:Nitric Oxide Synthase; D002118:Calcium