A nitrosyl complex of Mn-II-porphyrinate, [(F20TPP)- Mn-II(NO)], 1 (F20TPPH2 = 5,10,15,20 tetrakis(pentafluorophenyl)-porphyrin), was synthesized and characterized. Spectroscopic and structural characterization revealed complex 1 as a penta-coordinated Mn-II-nitrosyl with a linear Mn-N-O (180.0 degrees) moiety. Complex 1 does not react with O-2. However, it reacts with superoxide (O-2(-)) in THE at -80 degrees C to result in the corresponding nitrate (NO3-) complex, 2, via the formation of a presumed Mn-III-peroxynitrite intermediate. ESI-mass spectrometry and UV-visible and X-band EPR spectroscopic studies suggest the generation of Mn-IV-oxo species in the reaction through homolytic cleavage of the O-O bond of the peroxynitrite ligand as proposed in NOD activity. The intermediate formation of the Mni(III)-peroxynitrite was further supported by the well accepted phenol ring nitration which resembles the biologically well-established tyrosine nitration.