FeTMPyP is a synthetic porphyrin complexed with iron, which acts as a peroxynitrite decomposition catalyst. The rate constant for decomposition of peroxynitrite by FeTMPyP is 2.2 x 106 M−1s−1 with a turnover number of 360 ± 170 s−1. The predominant product (>90%) of this reaction is nitrate, with a minor amount of nitrite also formed (~6%), at pH 7.4.