Vb. O'Donnell et al., Catalytic consumption of nitric oxide by prostaglandin H synthase-1 regulates platelet function, J BIOL CHEM, 275(49), 2000, pp. 38239-38244
Nitric oxide ((NO)-N-.) plays a central role in vascular homeostasis via re
gulation of smooth muscle relaxation and platelet aggregation. Although mec
hanisms for (NO)-N-. formation are well known, removal pathways are less we
ll characterized, particularly in cells that respond to (NO)-N-. through ac
tivation of soluble guanylate cyclase. Herein, we report that (NO)-N-. is c
atalytically consumed by prostaglandin H synthase-1 (PGHS-1) through acting
as a reducing peroxidase substrate. With purified ovine PGHS-1, (NO)-N-. c
onsumption requires peroxide (LOOH or H2O2), with a K-m ((app)) for 15(S)hy
droperoxyeicosatetraenoic acid (HPETE) of 3.27 +/- 0.35 muM. During this, 2
mol (NO)-N-. are consumed per mol HPETE, and loss of HPETE hydroperoxy gro
up occurs with retention of the conjugated diene spectrum. Hydroperoxide-st
imulated (NO)-N-. consumption requires heme incorporation, is not inhibited
by indomethacin, and is further stimulated by the reducing peroxidase subs
trate, phenol. PGHS-1-dependent (NO)-N-. consumption also occurs during ara
chidonate, thrombin, or A23187 activation of platelets (1-2 muM.min(-1) for
typical plasma platelet concentrations) and prevents (NO)-N-. stimulation
of platelet soluble guanylate cyclase. Platelet sensitivity to (NO)-N-. as
an inhibitor of aggregation is greater using a platelet-activating stimulus
(U46619) that does not cause (NO)-N-. consumption, indicating that this me
chanism overcomes the anti-aggregatory effects of (NO)-N-., Catalytic consu
mption of (NO)-N-. during eicosanoid synthesis thus represents both a novel
pro-aggregatory function for PGHS-1 and a regulated mechanism for vascular
(NO)-N-. removal.