Abstract
Reaction between NO• and manganese tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnIIITE-2-PyP5+) was investigated at 25°C. At high excess of NO• (1.5 mM) the reaction with the oxidized, air-stable form MnIIITE-2-PyP5+ (5 μM), proceeds very slowly (t1/2 ≅ 60 min). The presence of excess ascorbate (1 mM) produces the reduced form, MnIITE-2-PyP4+, which reacts with NO• stoichiometrically and in the time of mixing (k ≅ 1 × 106 M−1 s−1). The high rate of formation and the stability of the product, MnIITE-2-PyP(NO)4+ ({Mn(NO)}6), make the reaction outcompete the reaction of NO• with O2. Our in vitro measurements show a linear absorbance response upon addition of NO to a PBS, pH 7.4, solution containing an excess of ascorbate over MnIIITE-2-PyP5+. Thus, the observed interactions can be the basis of a convenient and sensitive spectrophotometric assay for NO•. Also, it may have important implications for the in vivo behavior of MnIIITE-2-PyP5+ which is currently exploited as a possible therapeutic agent for various oxygen-radical related disorders.
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