title: Cardiolipin modulates allosterically the nitrite reductase activity of horse heart cytochrome c.
abstract: Upon cardiolipin (CL) liposomes binding, horse heart cytochrome c (cytc) changes its tertiary structure disrupting the heme-Fe-Met80 distal bond, reduces drastically the midpoint potential, binds CO and NO with high affinity, displays peroxidase activity, and facilitates peroxynitrite isomerization. Here, the effect of CL liposomes on the nitrite reductase activity of ferrous cytc (cytc-Fe(II)) is reported. In the absence of CL liposomes, hexa-coordinated 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 and 20.0 °C). However, CL liposomes facilitate the NO2 (-)-mediated nitrosylation of cytc-Fe(II) in a dose-dependent manner inducing the penta-coordination of the heme-Fe(II) atom. The value of k on for the NO2 (-)-mediated conversion of CL-cytc-Fe(II) to CL-cytc-Fe(II)-NO is 2.6 ± 0.3 M(-1) s(-1) (at pH 7.4 and 20.0 °C). Values of the apparent dissociation equilibrium constant for CL liposomes binding to cytc-Fe(II) are (2.2 ± 0.2) × 10(-6) M, (1.8 ± 0.2) × 10(-6) M, and (1.4 ± 0.2) × 10(-6) M at pH 6.5, 7.4, and 8.1, respectively, and 20.0 °C. These results suggest that the NO2 (-)-mediated conversion of CL-cytc-Fe(II) to CL-cytc-Fe(II)-NO could play anti-apoptotic effects impairing lipid peroxidation and therefore the initiation of the cell death program by the release of pro-apoptotic factors (including cytc) in the cytoplasm.
authors: Interdepartmental Laboratory for Electron Microscopy, University Roma Tre, Via della Vasca Navale 79, 00146, Rome, Italy, ascenzi@uniroma3.it.
authors: Paolo
authors: P
authors: Ascenzi
authors: Maria
authors: M
authors: Marino
authors: Fabio
authors: F
authors: Polticelli
authors: Roberto
authors: R
authors: Santucci
authors: Massimo
authors: M
authors: Coletta
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D002308:Cardiolipins / Q000378:metabolism*; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism*; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006736:Horses / Q000378:metabolism*; D008958:Models, Molecular; D009206:Myocardium / Q000201:enzymology* / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D009572:Nitrite Reductases / Q000737:chemistry / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D009585:Nitrogen Dioxide / Q000378:metabolism; D017434:Protein Structure, Tertiary
chemical_list: D002308:Cardiolipins; D009573:Nitrites; D009569:Nitric Oxide; D006418:Heme; D045304:Cytochromes c; D009572:Nitrite Reductases; D009585:Nitrogen Dioxide