Hänsch Robert, Lang Christina, Riebeseel Erik, Lindigkeit Rainer, Gessler Arthur, Rennenberg Heinz, Mendel Ralf R
Department of Plant Biology, Technical University of Braunschweig, 38023 Braunschweig, Germany.
J Biol Chem. 2006 Mar 10;281(10):6884-8. doi: 10.1074/jbc.M513054200. Epub 2006 Jan 5.
Sulfite oxidase (EC 1.8.3.1) from the plant Arabidopsis thaliana is the smallest eukaryotic molybdenum enzyme consisting of a molybdenum cofactor-binding domain but lacking the heme domain that is known from vertebrate sulfite oxidase. While vertebrate sulfite oxidase is a mitochondrial enzyme with cytochrome c as the physiological electron acceptor, plant sulfite oxidase is localized in peroxisomes and does not react with cytochrome c. Here we describe results that identified oxygen as the terminal electron acceptor for plant sulfite oxidase and hydrogen peroxide as the product of this reaction in addition to sulfate. The latter finding might explain the peroxisomal localization of plant sulfite oxidase. 18O labeling experiments and the use of catalase provided evidence that plant sulfite oxidase combines its catalytic reaction with a subsequent non-enzymatic step where its reaction product hydrogen peroxide oxidizes another molecule of sulfite. In vitro, for each catalytic cycle plant SO will bring about the oxidation of two molecules of sulfite by one molecule of oxygen. In the plant, sulfite oxidase could be responsible for removing sulfite as a toxic metabolite, which might represent a means to protect the cell against excess of sulfite derived from SO2 gas in the atmosphere (acid rain) or during the decomposition of sulfur-containing amino acids. Finally we present a model for the metabolic interaction between sulfite and catalase in the peroxisome.
来自拟南芥的亚硫酸盐氧化酶（EC 1.8.3.1）是最小的真核钼酶，它由一个钼辅因子结合结构域组成，但缺乏脊椎动物亚硫酸盐氧化酶中已知的血红素结构域。脊椎动物的亚硫酸盐氧化酶是一种线粒体酶，以细胞色素c作为生理电子受体，而植物亚硫酸盐氧化酶定位于过氧化物酶体，且不与细胞色素c反应。在此，我们描述了一些结果，这些结果确定氧气是植物亚硫酸盐氧化酶的末端电子受体，除了硫酸盐外，过氧化氢是该反应的产物。后一发现可能解释了植物亚硫酸盐氧化酶在过氧化物酶体中的定位。18O标记实验和过氧化氢酶的使用提供了证据，表明植物亚硫酸盐氧化酶将其催化反应与随后的非酶步骤相结合，在该非酶步骤中其反应产物过氧化氢氧化另一分子的亚硫酸盐。在体外，对于每个催化循环，植物亚硫酸盐氧化酶将通过一分子氧气使两分子亚硫酸盐氧化。在植物中，亚硫酸盐氧化酶可能负责去除作为有毒代谢物的亚硫酸盐，这可能是一种保护细胞免受大气中（酸雨）SO2气体或含硫氨基酸分解过程中产生的过量亚硫酸盐影响的手段。最后，我们提出了过氧化物酶体中亚硫酸盐与过氧化氢酶之间代谢相互作用的模型。
