Nitrosylation of manganese(II) tetrakis(N-ethylpyridinium-2-yl)porphyrin:: A simple and sensitive spectrophotometric assay for nitric oxide

Reaction between NO. and manganese tetrakis(N-ethylpyridinium-2-yl)porphyrin ((MNTE)-T-III-2-PyP5+) was investigated at 25 degreesC, At high excess of NO. (1.5 mM) the reaction with the oxidized, air-stable form (MnTE)-T-III-2-PyP5+ (5 muM), proceeds very slowly (t(1/2) congruent to 60 min), The presence of excess ascorbate (1 mM) produces the reduced form, (MnTE)-T-II-2-PyP4+, which reacts with NO. stoichiometrically and in the time of mixing (k congruent to 1 x 10(6) M-1 s(-1)). The high rate of formation and the stability of the product, (MnTE)-T-III-2-PyP(NO)(4+) ({Mn(NO)}(6)), make the reaction outcompete the reaction of NO. with O-2. 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 (MnTE)-T-III-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 (MnTE)-T-III-2-PyP5+ which is currently exploited as a possible therapeutic agent for various oxygen-radical related disorders. (C) 2000 Academic Press.