Br. Babu et Ow. Griffith, N-5-(1-IMINO-5-BUTENYL)-L-ORNITHINE - A NEURONAL ISOFORM SELECTIVE MECHANISM-BASED INACTIVATOR OF NITRIC-OXIDE SYNTHASE, The Journal of biological chemistry, 273(15), 1998, pp. 8882-8889
Nitric oxide synthase (NOS) catalyzes the NADPH-and O-2-dependent conv
ersion of L-arginine to nitric oxide (NO) and citrulline; three isofor
ms, the neuronal (nNOS), endothelial, and inducible, have been identif
ied. Because overproduction of NO is known to contribute to several pa
thophysiological conditions, NOS inhibitors are of interest as potenti
al therapeutic agents, Inhibitors that are potent, mechanism-based, an
d relatively selective for the NOS isoform causing pathology are of pa
rticular interest, In the present studies we report that vinyl-L-NIO (
N-5-(1-imino-3-butenyl)-L-ornithine; L-VNIO) binds to and inhibits nNO
S in competition with L-arginine (K-i = 100 nM); binding is accompanie
d by a type I optical difference spectrum consistent with binding near
the heme cofactor without interaction as a sixth axial heme ligand. S
uch binding is fully reversible, However, in the presence of NADPH and
O-2, L-VNIO irreversibly inactivates nNOS (K-inact = 0.078 min(-1); K
-I = 90 nM); inactivation is Ca2+/calmodulin-dependent. The cytochrome
c reduction activity of the enzyme is not affected by such treatment,
but the L-arginine-independent NADPH oxidase activity of nNOS is lost
in parallel with the overall activity. Spectral analyses establish th
at the nNOS heme cofactor is lost or modified by L-VNIO-mediated mecha
nism-based inactivation of the enzyme, The inducible isoform of NOS is
not inactivated by L-VNIO, and the endothelial isoform requires 20-fo
ld higher concentrations to attain similar to 75% of the rate of inact
ivation seen with nNOS, Among the NOS inactivating L-arginine derivati
ves, L-VNIO is the most potent and nNOS-selective reported to date.