In vitro formation of S-nitrosohemoglobin in red cells by inducible nitricoxide synthase

The present study demonstrates that NO produced in vitro by inducible nitri c oxide synthase in red cells can convert hemoglobin contained in the red c ells to S-nitrosohemoglobin, Experiments carried out either in the absence or in the presence of a low molecular weight thiol, such as cysteine, showe d that in the first case the target of NO is heme-Fe2+. On the contrary, in the presence of cysteine, the first step is the formation of S-nitrosocyst eine, followed by transfer of the NO group to a particular cysteine residue of P-globin, cysteine 93, These results confirm previous data indicating t he preferential formation of S-nitrosohemoglobin at that site by chemical m ethods [Ferranti et al, (1997) FEES Lett, 400, 17-24], and the existence of a physiological mechanism of inactivation for NO circulating in blood. The analysis of S-nitrosohemoglobin can also allow the quantification of the N O levels in blood to be applied for in vitro and in vivo measurements. (C) 1999 Federation of European Biochemical Societies.