Wilkinson Shane R, Obado Samson O, Mauricio Isabel L, Kelly John M
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK.
Proc Natl Acad Sci U S A. 2002 Oct 15;99(21):13453-8. doi: 10.1073/pnas.202422899. Epub 2002 Sep 26.
In most aerobic organisms hemoperoxidases play a major role in H(2)O(2)-detoxification, but trypanosomatids have been reported to lack this activity. Here we describe the properties of an ascorbate-dependent hemoperoxidase (TcAPX) from the American trypanosome Trypanosoma cruzi. The activity of this plant-like enzyme can be linked to the reduction of the parasite-specific thiol trypanothione by ascorbate in a process that involves nonenzymatic interaction. The role of heme in peroxidase activity was demonstrated by spectral and inhibition studies. Ascorbate could saturate TcAPX activity indicating that the enzyme obeys Michaelis-Menten kinetics. Parasites that overexpressed TcAPX activity were found to have increased resistance to exogenous H(2)O(2). To determine subcellular location an epitope-tagged form of TcAPX was expressed in T. cruzi, which was observed to colocalize with endoplasmic reticulum resident chaperone protein BiP. These findings identify an arm of the oxidative defense system of this medically important parasite. The absence of this redox pathway in the human host may be therapeutically exploitable.
在大多数需氧生物中，血红蛋白过氧化物酶在过氧化氢解毒过程中起主要作用，但据报道锥虫缺乏这种活性。在这里，我们描述了来自美洲锥虫克氏锥虫的一种抗坏血酸依赖性血红蛋白过氧化物酶（TcAPX）的特性。这种类似植物的酶的活性可以与抗坏血酸在一个涉及非酶相互作用的过程中还原寄生虫特异性硫醇锥虫硫醇联系起来。通过光谱和抑制研究证明了血红素在过氧化物酶活性中的作用。抗坏血酸可以使TcAPX活性饱和，表明该酶符合米氏动力学。发现过表达TcAPX活性的寄生虫对外源过氧化氢的抗性增加。为了确定亚细胞定位，在克氏锥虫中表达了一种表位标记形式的TcAPX，观察到它与内质网驻留伴侣蛋白BiP共定位。这些发现确定了这种医学上重要的寄生虫氧化防御系统的一个分支。人类宿主中这种氧化还原途径的缺失可能在治疗上具有可利用性。
