Hörtensteiner S, Wüthrich K L, Matile P, Ongania K H, Kräutler B
Department of Plant Biology, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland.
J Biol Chem. 1998 Jun 19;273(25):15335-9. doi: 10.1074/jbc.273.25.15335.
Chlorophyll breakdown in green plants is a long-standing biological enigma. Recent work has shown that pheophorbide a (Pheide a) derived from chlorophyll (Chl) is converted oxygenolytically into a primary fluorescent catabolite (pFCC-1) via a red Chl catabolite (RCC) intermediate. RCC, the product of the ring cleavage reaction catalyzed by Pheide a oxygenase, which is suggested to be the key enzyme in Chl breakdown in green plants, is converted into pFCC-1 by a reductase. In the present study, an in vitro assay comprising 18O2 Pheide a oxygenase and RCC reductase yielded labeled pFCC-1. Fast atom bombardment-mass spectrometric analysis of the purified pFCC-1 product revealed that only one of the two oxygen atoms newly introduced into Pheide a in the course of the cleavage reaction is derived from molecular oxygen. Analysis of the fragment ions located the oxygen atom derived from molecular oxygen on the formyl group of pyrrole B. This finding demonstrates that the cleavage of Pheide a in vascular plants is catalyzed by a monooxygenase. Chlorophyll breakdown is therefore indicated to be mechanistically related in higher plants and in the green alga Chlorella protothecoides.
绿色植物中的叶绿素分解是一个长期存在的生物学谜团。最近的研究表明，源自叶绿素（Chl）的脱镁叶绿酸a（Pheide a）通过红色叶绿素分解产物（RCC）中间体被氧解转化为初级荧光分解产物（pFCC-1）。RCC是由脱镁叶绿酸a加氧酶催化的环裂解反应的产物，该酶被认为是绿色植物中叶绿素分解的关键酶，它通过还原酶转化为pFCC-1。在本研究中，包含18O2脱镁叶绿酸a加氧酶和RCC还原酶的体外测定产生了标记的pFCC-1。对纯化的pFCC-1产物进行快速原子轰击质谱分析表明，在裂解反应过程中，新引入脱镁叶绿酸a的两个氧原子中只有一个来自分子氧。对碎片离子的分析将来自分子氧的氧原子定位在吡咯B的甲酰基上。这一发现表明维管植物中脱镁叶绿酸a的裂解是由单加氧酶催化的。因此，表明高等植物和绿藻原球藻中的叶绿素分解在机制上是相关的。
