SELECTIVE-INHIBITION OF CONSTITUTIVE NITRIC-OXIDE SYNTHASE BY L-N(G)-NITROARGININE

L-N(G)-Nitroarginine (NA) inhibited both the L-arginine oxidation and the L-arginine-independent NADPH oxidation reactions catalyzed by the calcium/calmodulin-dependent constitutive nitric oxide synthase (cNOS) from bovine brain. NA binding did not require calmodulin, calcium, or NADPH. The onset of inhibition was slow with a second-order associati on rate constant (k(on)) of 4.4 x 10(4) M-1 s-1. The dissociation rate constant (k(off)) was 6.5 x 10(-4) s-1. The K(d) value (k(off)/k(on)) of bovine brain cNOS for NA was 15 nM. L-Arginine was a competitive i nhibitor of NA binding with a K(s) value of 0.8 muM. The K(m) for L-ar ginine in the cNOS reaction was 1.2 muM. The NA binding sites of cNOS were titrated with NA, which enabled a k(cat) of 0.7 s-1, for the oxid ation Of L-arginine, to be calculated. Finally, a brain cNOS-(H-3)NA c omplex was isolated. In contrast to the potent and slow onset of NA in hibition of brain cNOS, NA inhibition of inducible mouse macrophage NO S (iNOS) was weaker (K(i) = 4.4 muM) and rapidly reversible. Thus, NA was a 300-fold more potent inhibitor of bovine brain cNOS than mouse m acrophage iNOS.