Ferric microperoxidase-11 catalyzes peroxynitrite isomerization

Microperoxidase-11 (MP11) is an undecapeptide derived from horse heart cytochrome c offering the possibility to study the reactivity of the heme group relatively unshielded by the protein. Here, the peroxynitrite isomerizadon to NO3- catalyzed by ferric MP11 (MP11-Fe(III)) is reported. Data were obtained between pH 3.6 and 8.1, at 20.0 degrees C. The value of the second-order rate constant (k(on)) for peroxynitrite isomerization to NO3- by MP11-Fe(III) decreases from (1.1 +/- 0.1) x 10(5) M-1 s(-1), at pH 3.6, to (6.1 +/- 0.6) x 10(3) M(-1)s(-1), at pH 8.1.The pH dependence of k(on) (pK(a) = 6.9) suggests that peroxynitrous acid reacts preferentially with MP11-Fe(III). The MP11-Fe(III)-catalyzed isomerization of peroxynitrite to NO3- has been ascribed to the reactive penta-coordinated heme-Fe atom of MP11-Fe(III). In fact, cyanide binding to the sixth coordination position of the heme-Fe atom inhibits the MP11-Fe(III)-catalyzed isomerization of peroxynitrite to NW. The values of the first-order rate constant (K-0) for isomerization of peroxynitrite to NO3- in the presence of the MP11-Fe(III)-CN complex are superimposable to those obtained in the absence of MP-Fe(III). Values of k(on) for peroxynitrite isomerization to NO3- by MP11-Fe(III) overlap those obtained for penta-coordinated cardiolipin-cytochrome c complex and for carboxymethylated cytochrome c in absence and presence of cardiolipin. Present results highlight the role of the heme-Fe(III) co-ordination state in the modulation of cytochrome c reactivity. (C) 2014 Elsevier Inc. All rights reserved.