Ii. Lobysheva et al., REDOX REACTIONS AND STABILITY OF DINITROSYL IRON COMPLEXES WITH THIOLATE LIGANDS AS POTENTIAL DONORS AND CARRIERS OF NITRIC-OXIDE, Biochemistry, 62(7), 1997, pp. 801-808
The effect of free thiols on the redox properties and stability of mon
omeric al-td dimeric forms of dinitrosyl iron complexes (DNIC) with cy
steine and glutathione under aerobic and anaerobic conditions has been
studied. DNIC containing cysteine and glutathione are dimeric in solu
tions at low concentration of free thiols and monomeric when the iron/
thiol ratio is lower than 1:20. Dimerization has been shown to affect
redox properties of DNIC. Optical spectra of dimeric and monomeric for
ms undergo similar changes after DNIC reduction with sodium dithionite
. Absorption maxima at 310 and 360 nm characteristic for dimeric forms
of DNIC disappear and two bands at 460 and 660 nm are observed. Forma
tion of a new band at 570 nm following the disappearance of these band
s in dimeric forms is characterized with k = (3.4 +/- 0.5).10(-3) sec(
-1). The formation of this complex is not revealed for monomers. The s
tability of tile initial and reduced complexes has been studied by EPR
and Mossbauer spectroscopy. It is shown to be determined essentially
by anionic ligands. Reduction of the complex does not affect its stabi
lity under aerobic conditions. The intermediate complexes formed under
aerobic conditions at low concentrations of sodium dithionite are les
s stable, however a reduced dimeric form characterized by an absorptio
n band at 570 nm is as stable as the initial form. The study revealed
that DNIC stability in the body is strongly dependent on the concentra
tion of free thiol groups, the redox potential of the environment, and
oxygen concentration. Thus it can regulate release and accumulation o
f nitric oxide in tissues.