Jm. Griscavage et al., INDUCIBLE NITRIC-OXIDE SYNTHASE FROM A RAT ALVEOLAR MACROPHAGE CELL-LINE IS INHIBITED BY NITRIC-OXIDE, The Journal of immunology, 151(11), 1993, pp. 6329-6337
The objective of this study was to determine whether inducible nitric
oxide (NO) synthase from a rat alveolar macrophage cell line (NR8383)
activated by LPS plus IFN-gamma could be regulated by NO, one of the t
wo products of the enzymatic reaction. This study was based on previou
s observations in this laboratory that NO is a negative feedback modul
ator of constitutive NO synthase from rat cerebellum. NO synthase acti
vity was determined by monitoring the formation of H-3-L-citrulline fr
om H-3-L-arginine in the presence of added cofactors. NO synthase cata
lyzed the conversion Of L-arginine to equimolar quantities of NO and L
-Citrulline. NO and S-nitrosothiols inhibited NO synthase activity and
this effect was enhanced by superoxide dismutase and attenuated by ox
yhemoglobin. Nitrite and nitrate, the oxidation products of NO, as wel
l as L-citrulline, the amino acid end-product, produced no significant
effects on NO synthase activity. The inhibitory effect of NO on NO sy
nthase appeared to be partially reversible upon addition of oxyhemoglo
bin. The inhibitory effect of NO was mimicked by other heme ligands in
cluding carbon monoxide, cyanide, and manganese-protoporphyrin IX. The
se observations indicate that (1) enzyme-bound heme plays a mechanisti
c role in the catalytic conversion of L-arginine to NO plus L-citrulli
ne; (2) NO may function as a negative feedback modulator of inducible
NO synthase by interacting with enzyme-bound heme; and (3) negative fe
edback modulation by NO may represent a mechanism by which the potenti
ally toxic L-arginine-NO pathway in activated alveolar macrophages is
turned off.