Ascenzi Paolo, Marino Maria, Ciaccio Chiara, Santucci Roberto, Coletta Massimo
Interdepartmental Laboratory of Electron Microscopy, Roma Tre University, Roma, Italy.
IUBMB Life. 2014 Jun;66(6):438-47. doi: 10.1002/iub.1283. Epub 2014 Jun 30.
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.
天然马心脏细胞色素c（cytc）对配体的反应性非常低，且不具有催化特性。然而，在与牛心磷脂（CL）结合后，cytc获得了类似肌红蛋白的特性。在此，报道了在20℃下，pH值在7.2至9.5之间NO与CL-cytc(III)的结合情况。在pH 7.2时，CL-cytc(III)发生可逆的亚硝基化反应，而在pH 7.9至9.5之间，CL-cytc(III)发生不可逆的还原亚硝基化反应，导致形成CL-cytc(II)-NO。在所研究的整个pH范围内，NO与CL-cytc(III)结合的一级动力学（k = 9.3 s(-1)）表明，配体结合受弱血红素-铁远端键断裂的限制。在pH 7.9至9.5之间，亚硝基化的CL-cytc(III)转化为无配体的亚铁衍生物（CL-cytc(II)），此过程依赖于pH值（hOH- = 3.0 × 10(3) M(-1) s(-1)）。然后，在NO过量的情况下，CL-cytc(II)转化为亚硝基化的CL-cytc(II)。CL-cytc(II)亚硝基化的二级速率常数的值基本与pH值无关，lon的平均值为1.4 × 10(7) M(-1) s(-1)。这些结果与CL-cytc亚硝基化可能在细胞凋亡调节中起作用的观点一致。
