NO2−-mediated nitrosylation of ferrous microperoxidase-11

Microperoxidase-11 (MP11) is an undecapeptide derived from horse heart cytochrome c (cyt c) and characterized by a covalently-linked solvent-exposed heme group. Here, kinetics of the NO2−-mediated nitrosylation of ferrous MP11 (MP11-Fe(II)) is reported. Data were obtained between pH6.4 and 8.2, at 20.0°C. The NO2−-mediated conversion of MP11-Fe(II) to MP11-Fe(II)-NO requires one proton; accordingly, values of the apparent second-order rate constant (kon) decrease by about two orders of magnitude from (2.9±0.3)×101M−1s−1 to (5.0±0.6)×10−1M−1s−1 upon increasing pH from 6.4 to pH8.2. The slope of the linear fitting of Logkon versus pH is −1.00±0.06. Values of kon for the NO2−-mediated nitrosylation of MP11-Fe(II) are similar to those of penta-coordinated cardiolipin-bound horse heart cyt c, exceeding by about two orders of magnitude those of wild-type horse heart cyt c. Present results highlight the role of heme distal residues in modulating horse heart cyt c reactivity. Microperoxidase-11 (MP11) is an undecapeptide derived from cytochrome c playing a primary role for dissecting the distinct contributions of the protein moiety and of the metal catalytic center. In fact, ferrous penta-coordinated MP11 catalyzes the conversion of NO2− to NO, followed by heme-Fe(II) nitrosylation, whereas hexa-coordinated cytochrome c is unreactive. [Display omitted] •Microperoxidase-11 is an undecapeptide derived from horse heart cytochrome c.•The heme-Fe atom of ferrous microperoxidase-11 is unshielded by the protein.•The heme-Fe atom of ferrous microperoxidase-11 is penta-coordinated and is highly reactive.•Ferrous microperoxidase-11 catalyzes the conversion of NO2− to NO.•NO2− induces the nitrosylation of ferrous microperoxidase-11.