Kruse E, Mock H P, Grimm B
Institut für Pflanzengenetik und Kulturpflanzenforschung, Gatersleben, Germany.
Planta. 1995;196(4):796-803.
Coproporphyrinogen III oxidase (coprogen oxidase; EC 1.3.3.3) is part of the pathway from 5-amino-levulinate to protoporphyrin IX which is common in all organisms and catalyses oxidative decarboxylation at two tetrapyrrole side chains. We cloned and sequenced full-length cDNAs encoding coprogen oxidase from barley (Hordeum vulgare L.) and tobacco (Nicotiana tabacum L.). They code for precursor peptides of 43.6 kDa and 44.9 kDa, respectively. Import into pea plastids resulted in a processed tobacco protein of approx. 39 kDa, which accumulated in the stroma fraction. Induction of synthesis of recombinant putative tobacco mature coprogen oxidase consisting of 338 amino-acid residues in Escherichia coli at 20 degrees C result in a catalytically active protein of approx. 39 kDa, while induction of its formation at 37 degrees C immediately terminated bacterial growth, possibly due to toxic effects on the metabolic balance of tetrapyrrole biosynthesis. The plant coprogen oxidase gene was expressed to different extents in all tissues investigated. This is most likely due to the differing requirements for tetrapyrroles in different organs. The steady-state level of mRNA did not significantly differ in etiolated and greening barley leaves. The content of coprogen oxidase RNA reached its maximum in developing cells and decreased drastically when cells were completely differentiated. Functioning of the two photosystems apparatus requires the synthesis of all pigment and protein components during plant development. It is speculated that the enzymes involved in tetrapyrrole synthesis are developmentally rather than light-dependently regulated. Regulation of these enzymes also guarantees a constant flux of metabolic intermediates and avoids photodynamic damage by accumulating porphyrins.
粪卟啉原III氧化酶（粪卟啉原氧化酶；EC 1.3.3.3）是从5-氨基乙酰丙酸到原卟啉IX途径的一部分，该途径在所有生物体中都很常见，并催化两个四吡咯侧链的氧化脱羧反应。我们从大麦（Hordeum vulgare L.）和烟草（Nicotiana tabacum L.）中克隆并测序了编码粪卟啉原氧化酶的全长cDNA。它们分别编码43.6 kDa和44.9 kDa的前体肽。导入豌豆质体后产生了一种约39 kDa的加工后的烟草蛋白，该蛋白积累在基质部分。在20℃下于大肠杆菌中诱导合成由338个氨基酸残基组成的重组推定烟草成熟粪卟啉原氧化酶，产生了一种约为39 kDa的具有催化活性的蛋白，而在37℃下诱导其形成则立即终止细菌生长，这可能是由于对四吡咯生物合成代谢平衡的毒性作用。植物粪卟啉原氧化酶基因在所研究的所有组织中均有不同程度的表达。这很可能是由于不同器官对四吡咯的需求不同。在黄化和绿化的大麦叶片中，mRNA的稳态水平没有显著差异。粪卟啉原氧化酶RNA的含量在发育中的细胞中达到最大值，而在细胞完全分化时急剧下降。在植物发育过程中，两个光系统装置的功能需要合成所有色素和蛋白质成分。据推测，参与四吡咯合成的酶是受发育调控而非光依赖调控的。对这些酶的调控还能保证代谢中间体的恒定通量，并通过积累卟啉避免光动力损伤。
