Role of thiols in the targeting of S-nitroso thiols to red blood cells.
We compared the nitric oxide (.NO)-releasing characteristics of two NO donors, the S-nitroso adduct of bovine serum albumin (BSANO) and the S-nitroso adduct of L-glutathione (GSNO). In oxygenated phosphate buffer (pH 7.4) and in hemoglobin solution, both NO donors released .NO only in the presence of a low molecular weight thiol (the most active was L-cysteine). The requirement of thiol to release .NO strongly suggests that a transnitrosation reaction occurs between the S-nitroso adduct of the NO donor and the sulfhydryl group of the NO acceptor. The reaction produced a labile S-nitroso-L-cysteine intermediate that released .NO. As shown by spin-trapping experiments, the transnitrosation reaction involved the formation of .NO (trapped by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide) and .S radicals (trapped by 5,5'-dimethyl-1-pyrroline N-oxide) of both the NO donors and the NO acceptor (L-cysteine). The reaction leading to .S radical formation was distinct from the transnitrosation reaction, since it was oxygen-dependent. We suggest that .S radicals are formed from oxidizing species produced after a reaction between .NO and molecular oxygen (.NO2 is a likely candidate). As for pure .NO gas, the major oxidation product of NO donors, in phosphate buffer (pH 7.4), was NO2-, with no formation of NO3-. In the presence of oxyhemoglobin, both NO donors produced only NO3-. BSANO and GSNO showed distinct patterns of .NO release both in phosphate buffer and in the presence of hemoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)
Pietraforte
D
D
Laboratorio di Biologia Cellulare, Istituto Superiore di Sanità, Roma, Italy.
Mallozzi
C
C
Scorza
G
G
Minetti
M
M
D002021:Buffers; D004578:Electron Spin Resonance Spectroscopy; D004912:Erythrocytes / Q000378:metabolism*; D016166:Free Radical Scavengers; D005609:Free Radicals; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008706:Methemoglobin / Q000378:metabolism; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism; D009603:Nitroso Compounds / Q000378:metabolism*; D010084:Oxidation-Reduction; D010710:Phosphates; D012710:Serum Albumin, Bovine / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000502:physiology*
D002021:Buffers; D016166:Free Radical Scavengers; D005609:Free Radicals; D006454:Hemoglobins; D009603:Nitroso Compounds; D010710:Phosphates; D013438:Sulfhydryl Compounds; D012710:Serum Albumin, Bovine; D009569:Nitric Oxide; D008706:Methemoglobin