Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, CNRS, F-75005, Paris, France.
Institut Universitaire de France, Paris, France.
Sci Rep. 2017 Aug 1;7(1):6973. doi: 10.1038/s41598-017-07305-6.
Magnesium is the metal at the center of all types of chlorophyll and is thus crucial to photosynthesis. When an element is involved in a biosynthetic pathway its isotopes are fractionated based on the difference of vibrational frequency between the different molecules. With the technical advance of multi-collectors plasma-mass-spectrometry and improvement in analytical precision, it has recently been found that two types of chlorophylls (a and b) are isotopically distinct. These results have very significant implications with regards to the use of Mg isotopes to understand the biosynthesis of chlorophyll. Here we present theoretical constraints on the origin of these isotopic fractionations through ab initio calculations. We present the fractionation factor for chlorphyll a, b, d, and f. We show that the natural isotopic variations among chlorophyll a and b are well explained by isotopic fractionation under equilibrium, which implies exchanges of Mg during the chlorophyll cycle. We predict that chlorophyll d and f should be isotopically fractionated compared to chlorophyll a and that this could be used in the future to understand the biosynthesis of these molecules.
镁是所有类型叶绿素的中心金属，因此对光合作用至关重要。当一种元素参与生物合成途径时，其同位素会根据不同分子之间振动频率的差异而分馏。随着多收集器等离子体质谱技术的进步和分析精度的提高，最近发现两种叶绿素（a 和 b）在同位素上存在明显差异。这些结果对于利用 Mg 同位素来理解叶绿素的生物合成具有非常重要的意义。在这里，我们通过从头计算对这些同位素分馏的起源提出了理论限制。我们提出了叶绿素 a、b、d 和 f 的分馏因子。我们表明，叶绿素 a 和 b 之间的天然同位素变化可以通过平衡下的同位素分馏很好地解释，这意味着在叶绿素循环期间发生了 Mg 的交换。我们预测，与叶绿素 a 相比，叶绿素 d 和 f 应该存在同位素分馏，这在未来可能用于理解这些分子的生物合成。
