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.
Vilhena
Fernando S D S
FS
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.
Louro
Sonia R W
SR
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