Hillebrand Henning, Schmidt Armin, Krauth-Siegel R Luise
Biochemie-Zentrum Heidelberg, Universität Heidelberg, 69120 Heidelberg, Germany.
J Biol Chem. 2003 Feb 28;278(9):6809-15. doi: 10.1074/jbc.M210392200. Epub 2002 Dec 3.
Trypanosoma brucei, the causative agent of African sleeping sickness, has three nearly identical genes encoding cysteine homologues of classical selenocysteine-containing glutathione peroxidases. The proteins are expressed in the mammalian and insect stages of the parasite. One of the genes, which contains a mitochondrial as well as a glycosomal targeting signal has been overexpressed. The recombinant T. brucei peroxidase has a high preference for the trypanothione/tryparedoxin couple as electron donor for the reduction of different hydroperoxides but accepts also T. brucei thioredoxin. The apparent rate constants k(2)' for the regeneration of the reduced enzyme are 2 x 10(5) m(-1) s(-1) with tryparedoxin and 5 x 10(3) m(-1) s(-1) with thioredoxin. No saturation kinetics was observed and the rate-limiting step of the overall reaction is reduction of the hydroperoxide. With glutathione, the peroxidase has marginal activity and reduction of the enzymes becomes limiting with a k(2)' value of 3 m (-1) s(-1). The T. brucei peroxidase, in contrast to the related Trypanosoma cruzi enzyme, also accepts hydrogen peroxide as substrate. The catalytic efficiency of the peroxidase studied here is comparable with that of the peroxiredoxin-like tryparedoxin peroxidases, which shows that trypanosomes possess two distinct peroxidase systems both dependent on the unique dithiol trypanothione.
布氏锥虫是非洲昏睡病的病原体，它有三个编码经典含硒半胱氨酸谷胱甘肽过氧化物酶半胱氨酸同源物的几乎相同的基因。这些蛋白质在寄生虫的哺乳动物和昆虫阶段表达。其中一个基因同时含有线粒体和糖体靶向信号，已被过量表达。重组布氏锥虫过氧化物酶高度优先选择锥虫硫醇/锥虫硫氧还蛋白对作为还原不同氢过氧化物的电子供体，但也接受布氏锥虫硫氧还蛋白。还原酶再生的表观速率常数k(2)'，与锥虫硫氧还蛋白反应时为2×10(5) m(-1) s(-1)，与硫氧还蛋白反应时为5×10(3) m(-1) s(-1)。未观察到饱和动力学，总反应的限速步骤是氢过氧化物的还原。对于谷胱甘肽，过氧化物酶活性微弱，酶的还原成为限速步骤，k(2)'值为3 m (-1) s(-1)。与相关的克氏锥虫酶不同，布氏锥虫过氧化物酶也接受过氧化氢作为底物。这里研究的过氧化物酶的催化效率与过氧化物还原酶样锥虫硫氧还蛋白过氧化物酶相当，这表明锥虫拥有两个不同的过氧化物酶系统，两者都依赖于独特的二硫醇锥虫硫醇。
