23S核糖體核糖核酸在二價鐵離子當作輔因子之下催化過氧化氫分解為氧氣

Abstract

核糖體被認為是一個生命的原始型態而且出現的時間更早於最早的共同祖先(last universal common ancestor, LUCA)。在古代地理學的地球史中，有個階段叫做大氧化事件，長達十億年將生物從無氧世界轉換至現今的有氧世界。在生物分子的演化當中，包括核糖體；如何在這過渡期中生存是至關重要的。此外，金屬在分子演化過程中扮演著不可或缺之角色，他給予生物分子各種不同的催化功能。我們假設23S核糖體核糖核酸(ribosomal RNA)的核糖體在有金屬離子，特別是正二價離子可以展現出各種不同的功能。在我的論文中，我測試23S rRNA是否有類過氧化氫酶(Catalase)的反應。過氧化氫酶幾乎在全部生物中都可以被發現，就像核糖體存在於所有生物當中。首先，過氧化氫酶的功能是保護細胞免於氧化壓力的破壞。過氧化氫酶的催化位是由含有鐵離子的紫質血紅素或者含有錳離子的雙核金屬簇(無血紅素的過氧化氫酶)所組成。結果顯示23S rRNA和二價鐵離子在特定的有氧條件下，可能可以催化過氧化氫解成氧氣。因此，可以說是為23S rRNA又增添一項催化功能。然而，這催化分解的功能在無氧狀態下是無法被觀察到的；進而推論23S rRNA在二價鐵離子當作輔因子之下，可能在大氧化事件的過渡期中，扮演著保護細胞免於氧化傷害攻擊的一個重要角色。

The ribosome predates the last universal common ancestor and is considered a primordial form of life. In the paleo-geographic history of the earth, there was a great oxidation event, which took biology one billion years to transit from anoxic world to modern (oxic) condition. The transition to be survived is crucial upon the evolution of biomolecules, including the ribosomes. Moreover, metals play imperative roles in the molecular evolution, conferred all sorts of catalytic functions on molecules. We hypothesize that the 23S ribosomal RNA (rRNA) of the ribosome exhibits a variety of catalytic functions with metal cations, beyond the Group II cations. Here I test the 23S rRNA with the catalase-like reactivity. Catalase, like the ribosome exists in all livings, is also found in nearly all living organisms. Primarily, the function of catalase is to protect cells against oxidative stress. The catalytic site of catalase is either comprised of porphyrin-heme with iron ion or a dinuclear metal cluster with manganese ion (non-heme catalase). The current settings for the 23S rRNA with Fe(II) in an oxic condition presumably catalyzes the decomposition of hydrogen peroxide into oxygen gas, thus expands the catalytic repertoire of the 23S rRNA. However, this catalytic decomposition is not observed in anoxic condition, suggests that the 23S rRNA with Fe(II) as a cofactor may shield cells from oxidative damages for biology during the transition of great oxidation event.