NG-ALLYL-L-ARGININE AND NG-CYCLOPROPYL-L-ARGININE - 2 NOVEL INHIBITORS OF MACROPHAGE NITRIC-OXIDE SYNTHASE

N(G)-Methyl-L-arginine has recently been shown to inactivate the inducible murine macrophage nitric oxide (.NO) synthase (Olken, N. M.; Rusche, K. M.; Richards, M. K.; Marletta, M. A. Biochem. Biophys. Res. Commun. 1991, 177, 828-833). N(G)-Allyl-L-arginine and N(G)-cyclopropyl-L-arginine were synthesized as potential mechanism-based enzyme inhibitors to exploit the chemistry presumed to occur at the active site. N(G)-Cyclopropyl-L-arginine was found to be a potent reversible inhibitor with a K(i) = 7.7-mu-M. N(G)-Allyl-L-arginine was found to be both a potent reversible (K(i) = 2.1-mu-M) and irreversible inhibitor of the enzyme. This irreversible inhibition demonstrated pseudo-first-order inactivation kinetics with k(inact) = 0.026 min-1 and K(I) = 3.4-mu-M. Stereospecific protection of the inactivation was afforded by L-arginine, and saturability of the inactivation rate was observed. Our studies indicate that both reversible and irreversible inhibition of the inducible .NO synthease can be achieved with relatively simple modifications of the substrate L-arginine.