Garg Harsh, Loughlin Patrick C, Willows Robert D, Chen Min
From the Australian Research Council Centre of Excellence for Translational Photosynthesis and School of Life and Environmental Sciences, University of Sydney, Sydney, New South Wales 2006, Australia and.
the Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia.
J Biol Chem. 2017 Nov 24;292(47):19279-19289. doi: 10.1074/jbc.M117.814756. Epub 2017 Sep 28.
Chlorophylls (Chls) are the most important cofactors for capturing solar energy to drive photosynthetic reactions. Five spectral types of Chls have been identified to date, with Chl having the most red-shifted absorption maximum because of a C2-formyl group substitution of Chl However, the biochemical provenance of this formyl group is unknown. Here, we used a stable isotope labeling technique (O and H) to determine the origin of the C2-formyl group of Chl and to verify whether Chl is synthesized from Chl in the cyanobacterial species In the presence of either HO or O, the origin of oxygen atoms in the newly synthesized chlorophylls was investigated. The pigments were isolated with HPLC, followed by MS analysis. We found that the oxygen atom of the C2-formyl group originates from molecular oxygen and not from HO. Moreover, we examined the kinetics of the labeling of Chl and Chl from grown in 50% DO-seawater medium under different light conditions. When cells were shifted from white light DO-seawater medium to far-red light HO-seawater medium, the observed deuteration in Chl indicated that Chl(ide) is the precursor of Chl Taken together, our results advance our understanding of the biosynthesis pathway of the chlorophylls and the formation of the formyl group in Chl .
叶绿素（Chls）是捕获太阳能以驱动光合作用反应的最重要辅助因子。迄今为止，已鉴定出五种光谱类型的叶绿素，其中叶绿素 由于叶绿素 的 C2-甲酰基取代而具有最大程度的红移吸收峰。然而，该甲酰基的生化来源尚不清楚。在这里，我们使用稳定同位素标记技术（O和H）来确定叶绿素 的 C2-甲酰基的来源，并验证叶绿素 是否由蓝藻物种中的叶绿素 合成。在存在HO或O的情况下，研究了新合成叶绿素中氧原子的来源。用高效液相色谱法分离色素，然后进行质谱分析。我们发现C2-甲酰基的氧原子来源于分子氧而非HO。此外，我们研究了在不同光照条件下，在50% DO-海水培养基中生长的 中叶绿素 和叶绿素 的标记动力学。当细胞从白光DO-海水培养基转移到远红光HO-海水培养基时，叶绿素 中观察到的氘化表明叶绿素（酸） 是叶绿素 的前体。综上所述，我们的结果推进了我们对叶绿素生物合成途径以及叶绿素 中甲酰基形成的理解。
