Hysteresis in thioredoxin-glutathione reductase (TGR) from the adult stage of the liver fluke Fasciola hepatica
Hysteresis in thioredoxin-glutathione reductase (TGR) from the adult stage of the liver fluke Fasciola hepatica
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DOI：
10.1016/j.parint.2011.01.005
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发表时间：
2011-06-01
影响因子：
1.9
通讯作者：
Rendon, Juan L.
中科院分区：
文献类型：
--
作者：
Guevara-Flores, Alberto;Pablo Pardo, Juan;Rendon, Juan L.
硫氧还蛋白-谷胱甘肽还原酶（TGR）是从肝片吸虫成虫阶段纯化的。在38 ℃和pH7.8时，以DTNB或GSSG为底物，比活性值分别为10.2 U mg（-1）和64.5 U mg（-1）。在相同条件下，表观Km值为46 +/- 8 μ M（DTNB）和30 +/- 5 μ M（GSSG）。该酶还能够催化硫醇/二硫键交换反应。获得61，000的亚基Mr。与绦虫的同源酶一样，在中等或高浓度的底物GSSG的酶测定中观察到滞后时间。在GSH的存在下，滞后行为被恢复，并显着依赖于pH值，这样的滞后时间的大小与介质的酸度增加。这些结果强烈表明，一个滞后的动力学是一个共同的特点，TGR从任何寄生扁形虫。序列比较显示，TGR特有的动力学行为起源的结构性半胱氨酸残基在F.肝酶基于这些观察结果，最近提出的解释TGR的GSSG依赖性滞后动力学的模型假设特定半胱氨酸残基通过谷胱甘肽化的共价修饰[Bonilla M.等人（2008）J Biol Chem 283：17898]需要重新评估。(C)2011爱思唯尔爱尔兰有限公司保留所有权利。
Thioredoxin-glutathione reductase (TGR) was purified from the adult stage of the liver fluke Fasciola hepatica. At 38 degrees C and pH 7.8, specific activity values were 10.2 U mg(-1) and 64.5 U mg(-1), with DTNB or GSSG as substrates, respectively. Under the same conditions, apparent Km values were 46 +/- 8 mu M (DTNB) and 30 +/- 5 mu M (GSSG). The enzyme was also able to catalyze thiol/disulfide exchange reactions. A subunit Mr of 61,000 was obtained. Like the homologous enzyme from the tapeworms, a lag time was observed in the enzyme assays at moderate or high concentrations of the substrate GSSG. The hysteretic behavior was reverted in the presence of GSH and was notably dependent on pH, such that the magnitude of the lag time increased with the acidity of the medium. These results strongly suggest that a hysteretic kinetic is a common feature of TGR from any parasitic flatworm. A sequence comparison revealed the structural cysteine residues proposed to be in the origin of the peculiar kinetic behavior of TGR are absent from the F. hepatica enzyme. Based on these observations, the model proposed recently to explain the GSSG-dependent hysteretic kinetic of TGR, which assumes the covalent modification of specific cysteine residues through glutathionylation [Bonilla M. et al. (2008) J Biol Chem 283: 17898] needs to be reevaluated. (C) 2011 Elsevier Ireland Ltd. All rights reserved.