Wilkinson Shane R, Taylor Martin C, Touitha Said, Mauricio Isabel L, Meyer David J, Kelly John M
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.
Biochem J. 2002 Jun 15;364(Pt 3):787-94. doi: 10.1042/BJ20020038.
Until recently, it had been thought that trypanosomes lack glutathione peroxidase activity. Here we report the subcellular localization and biochemical properties of a second glutathione-dependent peroxidase from Trypanosoma cruzi (TcGPXII). TcGPXII is a single-copy gene which encodes a 16 kDa protein that appears to be specifically dependent on glutathione as the source of reducing equivalents. Recombinant TcGPXII was purified and shown to have peroxidase activity towards a narrow substrate range, restricted to hydroperoxides of fatty acids and phospholipids. Analysis of the pathway revealed that TcGPXII activity could be readily saturated by glutathione and that the peroxidase functioned by a Ping Pong mechanism. Enzyme reduction was shown to be the rate-limiting step in this pathway. Using immunofluorescence, TcGPXII was shown to co-localize with a homologue of immunoglobulin heavy-chain binding protein (BiP), a protein restricted to the endoplasmic reticulum and Golgi. As the smooth endoplasmic reticulum is the site of phospholipid and fatty acid biosynthesis, this suggests that TcGPXII may play a specific role in the T. cruzi oxidative defence system by protecting newly synthesized lipids from peroxidation.
直到最近，人们一直认为锥虫缺乏谷胱甘肽过氧化物酶活性。在此我们报告来自克氏锥虫的第二种谷胱甘肽依赖性过氧化物酶（TcGPXII）的亚细胞定位和生化特性。TcGPXII是一个单拷贝基因，编码一种16 kDa的蛋白质，该蛋白质似乎特别依赖谷胱甘肽作为还原当量的来源。重组TcGPXII被纯化，并显示对狭窄的底物范围具有过氧化物酶活性，仅限于脂肪酸和磷脂的氢过氧化物。对该途径的分析表明，TcGPXII活性很容易被谷胱甘肽饱和，并且过氧化物酶通过乒乓机制起作用。酶还原被证明是该途径中的限速步骤。使用免疫荧光法，显示TcGPXII与免疫球蛋白重链结合蛋白（BiP）的同源物共定位，BiP是一种仅限于内质网和高尔基体的蛋白质。由于光滑内质网是磷脂和脂肪酸生物合成的场所，这表明TcGPXII可能通过保护新合成的脂质免受过氧化作用，在克氏锥虫氧化防御系统中发挥特定作用。
