title: Reductive nitrosylation of the cardiolipin-ferric cytochrome c complex.
abstract: Native horse heart cytochrome c (cytc) displays a very low reactivity toward ligands and does not exhibit catalytic properties. However, upon bovine cardiolipin (CL) binding, cytc achieves myoglobin-like properties. Here, NO binding to CL-cytc(III) between pH 7.2 and 9.5, at 20 °C, is reported. At pH 7.2, CL-cytc(III) undergoes reversible nitrosylation, whereas between pH 7.9 and 9.5 CL-cytc(III) undergoes irreversible reductive nitrosylation leading to the formation of CL-cytc(II)-NO. Over the whole pH range explored, first-order kinetics of NO binding to CL-cytc(III) (k = 9.3 s(-1) ) indicates that ligand binding is limited by the cleavage of the weak heme-Fe distal bond. Between pH 7.9 and 9.5, nitrosylated CL-cytc(III) converts to the ligand-free ferrous derivative (CL-cytc(II)), this process being pH-dependent (hOH-  = 3.0 × 10(3) M(-1) s(-1) ). Then, CL-cytc(II) converts to nitrosylated CL-cytc(II), in the presence of NO excess. The value of the second-order rate constant for CL-cytc(II) nitrosylation is essentially pH-independent, the average value of lon being 1.4 × 10(7) M(-1) s(-1) . These results agree with the view that CL-cytc nitrosylation may play a role in apoptosis regulation.
authors: Interdepartmental Laboratory of Electron Microscopy, Roma Tre University, Roma, Italy.
authors: Paolo
authors: P
authors: Ascenzi
authors: Maria
authors: M
authors: Marino
authors: Chiara
authors: C
authors: Ciaccio
authors: Roberto
authors: R
authors: Santucci
authors: Massimo
authors: M
authors: Coletta
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002308:Cardiolipins / Q000378:metabolism*; D002417:Cattle; D045304:Cytochromes c / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D002308:Cardiolipins; D046912:Multiprotein Complexes; D009569:Nitric Oxide; D006418:Heme; D045304:Cytochromes c; D007501:Iron
keywords: NO binding to the cardiolipin-ferric cytochrome c complex; NO binding to the cardiolipin-ferrous cytochrome c complex; cardiolipin-ferric cytochrome c complex; kinetics.; reductive nitrosylation