DIFAR, Università di Genova, Genoa, Italy.
Cell Mol Neurobiol. 2013 Jul;33(5):637-49. doi: 10.1007/s10571-013-9926-7. Epub 2013 Apr 9.
Vertebrate retinal rod outer segments (OS) consist of a stack of disks surrounded by the plasma membrane, where phototransduction takes place. Energetic metabolism in rod OS remains obscure. Literature described a so-called Mg(2+)-dependent ATPase activity, while our previous results demonstrated the presence of oxidative phosphorylation (OXPHOS) in OS, sustained by an ATP synthetic activity. Here we propose that the OS ATPase and ATP synthase are the expression of the same protein, i.e., of F1Fo-ATP synthase. Imaging on bovine retinal sections showed that some OXPHOS proteins are expressed in the OS. Biochemical data on bovine purified rod OS, characterized for purity, show an ATP synthase activity, inhibited by classical F1Fo-ATP synthase inhibitors. Moreover, OS possess a pH-dependent ATP hydrolysis, inhibited by pH values below 7, suggestive of the functioning of the inhibitor of F1 (IF1) protein. WB confirmed the presence of IF1 in OS, substantiating the expression of F1Fo ATP synthase in OS. Data suggest that the OS F1Fo ATP synthase is able to hydrolyze or synthesize ATP, depending on in vitro or in vivo conditions and that the role of IF1 would be pivotal in the prevention of the reversal of ATP synthase in OS, for example during hypoxia, granting photoreceptor survival.
脊椎动物视网膜视杆外段（OS）由被质膜包围的堆叠盘组成，光感受器在此处发生。视杆 OS 的能量代谢仍不清楚。文献描述了一种所谓的 Mg（2+）依赖性 ATP 酶活性，而我们之前的结果表明 OS 中存在氧化磷酸化（OXPHOS），由 ATP 合成活性维持。在这里，我们提出 OS ATP 酶和 ATP 合酶是同一种蛋白质的表达，即 F1Fo-ATP 合酶。对牛视网膜切片的成像表明，一些 OXPHOS 蛋白在 OS 中表达。对牛纯化视杆 OS 的生化数据进行了纯度特征分析，显示存在 ATP 合酶活性，被经典的 F1Fo-ATP 合酶抑制剂抑制。此外，OS 具有 pH 依赖性 ATP 水解，在 pH 值低于 7 时受到抑制，提示 F1 抑制剂（IF1）蛋白的功能。WB 证实 OS 中存在 IF1，证实了 OS 中 F1Fo ATP 合酶的表达。数据表明，OS 的 F1Fo ATP 合酶能够根据体外或体内条件水解或合成 ATP，并且 IF1 的作用在防止 OS 中 ATP 合酶的逆转（例如在缺氧期间）中至关重要，为光感受器的存活提供保障。
