Nitric oxide transfer from the NO-donor S-nitroso-N-acetylpenicillamine to monomers and dimers of water-soluble iron-porphyrins.
The nitrosylation of two water-soluble iron-porphyrins, the anionic Fe(III)-meso-tetrakis(p-sulfonatophenyl)porphyrin (FeTPPS(4)) and the cationic Fe(III)-meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (FeTMPyP), by the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) was studied using optical absorption spectroscopy. The influence of ionic and non-ionic micelles on rates of nitric oxide transfer was investigated. Initially, the effect of the micelles on the pH-dependent equilibrium between monomeric and micro-oxo-dimeric species of the iron-porphyrins was examined. It is not affected in micelle-porphyrin systems with electric charges identical in sign. The non-ionic micelles of polidocanol induce a small negative pK shift. In contrast, the dimerization equilibrium of porphyrins in oppositely charged micellar phases is displaced to lower pH by approximately 2 units. Nitric oxide binding to monomers and micro-oxo-dimers was examined at pH 5.0 and 8.0, respectively. Contrary to nitrosylation by NO gas, SNAP induces reductive nitrosylation. There was no observed NO-Fe(III)porphyrin intermediate. Nitrosylation rates were obtained and compared in aqueous buffer and in micellar systems. Monomers nitrosylate much faster than micro-oxo-dimers. Oppositely charged micelles prevent nitrosylation of the iron-porphyrins or considerably enhance nitrosylation times. Nitrosylation rates are comparable to transnitrosylation rates between several S-nitrosothiols and thiol-containing proteins, suggesting biological relevance for the process.
Department of Physics, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente, 225 Gávea, Rio de Janeiro, RJ CEP 22453.900, Brazil.
Fernando S D S
FS
Vilhena
Sonia R W
SR
Louro
D019281:Dimerization; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009569:Nitric Oxide / Q000737:chemistry* / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000737:chemistry* / Q000378:metabolism; D011166:Porphyrins / Q000737:chemistry* / Q000378:metabolism; D026423:S-Nitroso-N-Acetylpenicillamine / Q000737:chemistry* / Q000378:metabolism; D012995:Solubility; D013053:Spectrophotometry / Q000379:methods; D017186:Titrimetry
D005290:Ferric Compounds; D020030:Nitric Oxide Donors; D011166:Porphyrins; C092400:meso-tetrakis(4-sulfonatophenyl)porphyrin; D009569:Nitric Oxide; C021096:tetra(4-N-methylpyridyl)porphine; D026423:S-Nitroso-N-Acetylpenicillamine