Ferrimyoglobin at pH 7.4 binds nitric oxide to yield nitric oxide adducts.
In the presence of glutathione (GSH), nitrosoadducts of Mb(III) react with
it to give nitrosoglutathione, whose concentration has been determined with
an apparatus based on a specific and sensitive solid-state amperometric ga
s sensor. The reaction constant between the adduct and glutathione, k(GSH)
= (47 +/-1) M-1 s(-1), obtained by UV-Vis spectroscopy kinetic measurements
, is about one-eighth of the constant with OH- determined by other authors.
We can explain this fact with the higher nucleophilicity of OH- compared t
o GSH, due to the bulkiness and charge of the species. It is known that the
formation of nitrosothiols starting from nitrite or NO (nitrogen monoxide)
and glutathione, in the absence of oxygen, is impossible. Thus, from a bio
logical point of view, it is important to point out that GSH reacts with NO
in the presence of ferrimyoglobin, even at physiological pH, to form nitro
soglutathione. (C) 2001 Academic Press.