Madsen O, Sandal L, Sandal N N, Marcker K A
Department of Molecular Biology, University of Aarhus, Denmark.
Plant Mol Biol. 1993 Oct;23(1):35-43. doi: 10.1007/BF00021417.
In plants the enzyme coproporphyrinogen oxidase catalyzes the oxidative decarboxylation of coproporphyrinogen III to protoporphyrinogen IX in the heme and chlorophyll biosynthesis pathway(s). We have isolated a soybean coproporphyrinogen oxidase cDNA from a cDNA library and determined the primary structure of the corresponding gene. The coproporphyrinogen oxidase gene encodes a polypeptide with a predicted molecular mass of 43 kDa. The derived amino acid sequence shows 50% similarity to the corresponding yeast amino acid sequence. The main difference is an extension of 67 amino acids at the N-terminus of the soybean polypeptide which may function as a transit peptide. A full-length coproporphyrinogen oxidase cDNA clone complements a yeast mutant deleted of the coproporphyrinogen oxidase gene, thus demonstrating the function of the soybean protein. The soybean coproporphyrinogen oxidase gene is highly expressed in nodules at the stage where several late nodulins including leghemoglobin appear. The coproporphyrinogen oxidase mRNA is also detectable in leaves but at a lower level than in nodules while no mRNA is detectable in roots. The high level of coproporphyrinogen oxidase mRNA in soybean nodules implies that the plant increases heme production in the nodules to meet the demand for additional heme required for hemoprotein formation.
在植物中，粪卟啉原氧化酶在血红素和叶绿素生物合成途径中催化粪卟啉原III氧化脱羧生成原卟啉原IX。我们从一个cDNA文库中分离出了大豆粪卟啉原氧化酶cDNA，并确定了相应基因的一级结构。粪卟啉原氧化酶基因编码一种预测分子量为43 kDa的多肽。推导的氨基酸序列与相应的酵母氨基酸序列显示出50%的相似性。主要差异在于大豆多肽N端有67个氨基酸的延伸，这可能起到转运肽的作用。一个全长粪卟啉原氧化酶cDNA克隆可互补缺失粪卟啉原氧化酶基因的酵母突变体，从而证明了大豆蛋白的功能。大豆粪卟啉原氧化酶基因在包括豆血红蛋白在内的几种晚期结瘤素出现的阶段在根瘤中高度表达。在叶片中也可检测到粪卟啉原氧化酶mRNA，但水平低于根瘤，而在根中未检测到mRNA。大豆根瘤中粪卟啉原氧化酶mRNA的高水平表明，植物在根瘤中增加血红素的产生，以满足血红蛋白形成所需额外血红素的需求。
