Nv. Gorbunov et al., REDUCTION OF FERRYLMYOGLOBIN AND FERRYLHEMOGLOBIN BY NITRIC-OXIDE - APROTECTIVE MECHANISM AGAINST FERRYL HEMOPROTEIN-INDUCED OXIDATIONS, Biochemistry, 34(20), 1995, pp. 6689-6699
The reactions of metmyoglobin (metMb) and methemoglobin (metHb), oxidi
zed to their respective oxoferryl free radical species ((.)Mb-Fe-IV=O/
(.)Hb-4Fe(IV)=O) by tert-butyl hydroperoxide (t-BuOOH), with nitric ox
ide (NO.) were studied by a combination of optical, electron spin reso
nance (ESR), ionspray mass (MS), fluorescence, and chemiluminescence s
pectrometries to gain insight into the mechanism by which NO. protects
against oxidative injury produced by (.)Mb-Fe-IV=O/(.)Hb-4Fe(IV)=O. O
xidation of metMb/metHb by t-BuOOH in a nitrogen atmosphere proceeded
via the formation of two protein electrophilic centers, which were hem
e oxoferryl and the apoprotein radical centered at tyrosine (for the (
.)Mb-Fe-IV=O form, the g value was calculated to be 2.0057), and was a
ccompanied by the formation of t-BuOOH-derived tert-butyl(per)oxyl rad
icals. We hypothesized that NO. may reduce both oxoferryl and apoprote
in free radical electrophilic centers of (.)Mb-Fe-IV=O/(.)Hb-4Fe(IV)=O
and eliminate tert-butyl(per)oxyl radicals, thus protecting against o
xidative damage. We found that NO. reduced (.)Mb-Fe-IV=O/(.)Hb-4Fe(IV)
=O to their respective ferric (met) forms and prevented the following:
(i) oxidation of cis-parinaric acid (PnA) in liposomes, (ii) oxidatio
n of luminol, and (iii) formation of the tert-butyl(per)oxyl adduct wi
th the spin trap DMPO. NO. eliminated the signals of tyrosyl radical d
etected by ESR and oxoferryl detected by MS in the reaction of t-BuOOH
with metMb. As evidenced by MS of apomyoglobin, this effect was due t
o the two-electron reduction of (.)Mb-Fe-IV=O by NO. at the oxoferryl
center rather than to nitrosylation of the tyrosine residues. Results
of our in vitro experiments suggest that NO. exhibits a patent, target
able antioxidant effect against oxidative damage produced by oxoferryl
Mb/Hb.