title: The nitrite reductase activity of horse heart carboxymethylated-cytochrome c is modulated by cardiolipin.
abstract: Horse heart carboxymethylated cytc (CM-cytc) displays myoglobin-like properties. Here, the effect of cardiolipin (CL) liposomes on the nitrite reductase activity of ferrous CM-cytc [CM-cytc-Fe(II)], in the presence of sodium dithionite, is reported between pH 5.5 and 7.6, at 20.0 °C. Cytc-Fe(II) displays a very low value of the apparent second-order rate constant for the NO2 (-)-mediated conversion of cytc-Fe(II) to cytc-Fe(II)-NO [k on = (7.3 ± 0.7) × 10(-2) M(-1) s(-1); at pH 7.4], whereas the value of k on for NO2 (-) reduction by CM-cytc-Fe(II) is 1.1 ± 0.2 M(-1) s(-1) (at pH 7.4). CL facilitates the NO2 (-)-mediated nitrosylation of CM-cytc-Fe(II) in a dose-dependent manner, the value of k on for the NO2 (-)-mediated conversion of CL-CM-cytc-Fe(II) to CL-CM-cytc-Fe(II)-NO (5.6 ± 0.6 M(-1) s(-1); at pH 7.4) being slightly higher than that for the NO2 (-)-mediated conversion of CL-cytc-Fe(II) to CL-cytc-Fe(II)-NO (2.6 ± 0.3 M(-1) s(-1); at pH 7.4). The apparent affinity of CL for CM-cytc-Fe(II) is essentially pH independent, the average value of B being (1.3 ± 0.3) × 10(-6) M. In the absence and presence of CL liposomes, the nitrite reductase activity of CM-cytc-Fe(II) increases linearly on lowering pH and the values of the slope of the linear fittings of Log k on versus pH are -1.05 ± 0.07 and -1.03 ± 0.03, respectively, reflecting the involvement of one proton for the formation of the transient ferric form, NO, and OH(-). These results indicate that Met80 carboxymethylation and CL binding cooperate in the stabilization of the highly reactive heme-Fe atom of CL-CM-cytc.
authors.affiliation: Interdepartmental Laboratory for Electron Microscopy, Roma Tre University, Via della Vasca Navale 79, 00146, Rome, Italy. ascenzi@uniroma3.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma "Tor Vergata", Via Montpellier 1, 00133, Rome, Italy.|Interuniversity Consortium for the Research on the Chemistry of Metals in Biological Systems, Via Celso Ulpiani 27, 70126, Bari, Italy.
authors.forename: Diego
authors.initials: D
authors.lastname: Sbardella
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma "Tor Vergata", Via Montpellier 1, 00133, Rome, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Sinibaldi
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma "Tor Vergata", Via Montpellier 1, 00133, Rome, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Santucci
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma "Tor Vergata", Via Montpellier 1, 00133, Rome, Italy.|Interuniversity Consortium for the Research on the Chemistry of Metals in Biological Systems, Via Celso Ulpiani 27, 70126, Bari, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Coletta
mesh_terms: D000818:Animals; D002308:Cardiolipins / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism*; D005296:Ferrous Compounds / Q000378:metabolism; D006321:Heart; D006736:Horses; D008745:Methylation; D009572:Nitrite Reductases / Q000378:metabolism*
chemical_list: D002308:Cardiolipins; D005296:Ferrous Compounds; D045304:Cytochromes c; D009572:Nitrite Reductases
keywords: Cardiolipin liposomes; Horse heart carboxymethylated-cytochrome c; Kinetics; Nitrite reductase activity