Ascenzi Paolo, Marino Maria, Polticelli Fabio, Santucci Roberto, Coletta Massimo
Interdepartmental Laboratory for Electron Microscopy, University Roma Tre, Via della Vasca Navale 79, 00146, Rome, Italy,
J Biol Inorg Chem. 2014 Oct;19(7):1195-201. doi: 10.1007/s00775-014-1175-9. Epub 2014 Jun 27.
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.
与心磷脂（CL）脂质体结合后，马心脏细胞色素c（cytc）会改变其三级结构，破坏血红素 - 铁 - 蛋氨酸80的远端键，大幅降低中点电位，以高亲和力结合一氧化碳和一氧化氮，表现出过氧化物酶活性，并促进过氧亚硝酸盐异构化。在此，报告了CL脂质体对亚铁细胞色素c（cytc-Fe(II)）亚硝酸还原酶活性的影响。在没有CL脂质体的情况下，六配位的cytc-Fe(II)对于由NO2 (-)介导的cytc-Fe(II)转化为cytc-Fe(II)-NO的表观二级速率常数非常低（k on = (7.3 ± 0.7) × 10(-2) M(-1) s(-1)；在pH 7.4和20.0 °C）。然而，CL脂质体以剂量依赖的方式促进NO2 (-)介导的cytc-Fe(II)亚硝化，诱导血红素 - Fe(II)原子的五配位。对于由NO2 (-)介导的CL-cytc-Fe(II)转化为CL-cytc-Fe(II)-NO，k on的值为2.6 ± 0.3 M(-1) s(-1)（在pH 7.4和20.0 °C）。在pH 6.5、7.4和8.1以及20.0 °C时，CL脂质体与cytc-Fe(II)结合的表观解离平衡常数分别为(2.2 ± 0.2) × 10(-6) M、(1.8 ± 0.2) × 10(-6) M和(1.4 ± 0.2) × 10(-6) M。这些结果表明，NO2 (-)介导的CL-cytc-Fe(II)转化为CL-cytc-Fe(II)-NO可能发挥抗凋亡作用，损害脂质过氧化，从而通过细胞质中促凋亡因子（包括cytc）的释放来启动细胞死亡程序。
