Tzeng H F, Blackburn A C, Board P G, Anders M W
Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642, USA.
Chem Res Toxicol. 2000 Apr;13(4):231-6. doi: 10.1021/tx990175q.
Glutathione transferase zeta catalyzes the glutathione-dependent oxidation or conjugation of a range of alpha-haloacids. Repeated administration of dichloroacetate to human subjects increases its plasma elimination half-life, and the activity of glutathione transferase zeta is decreased in rats given dichloroacetate. The objective of the studies presented here was to investigate the kinetics and mechanism of the dichloroacetate-induced decrease in glutathione transferase zeta activity. The rate constants (k(inact)) for the dichloroacetate-dependent inactivation of glutathione transferase zeta in liver cytosol are in the following order: rat > mouse > human; the half-maximal inhibitory concentration (K(inact)) of DCA did not differ among the species that were studied. In contrast to dichloroacetate, chlorofluoroacetate produced much less inactivation of mouse liver glutathione transferase zeta activity. Moreover, the addition of N-acetyl-L-cysteine or potassium cyanide did not fully block the dichloroacetate-induced inactivation of glutathione transferase zeta. The k(inact) values for the dichloroacetate-induced inactivation of four polymorphic variants of recombinant human glutathione transferase zeta (hGSTZ1-1) were in the following order: variant 1a-1a < 1b-1b approximately 1c-1c approximately 1d-1d. The dichloroacetate-induced inactivation of hGSTZ1-1 was irreversible. The binding of radioactivity from [1-(14)C]dichloroacetate and from [(35)S]glutathione to recombinant hGSTZ1c-1c was demonstrated, indicating covalent modification of the protein. These results show that dichloroacetate is a mechanism-based inactivator of glutathione transferase zeta and is biotransformed to electrophilic metabolites that covalently modify and, thereby, inactivate the enzyme.
谷胱甘肽转移酶ζ催化一系列α-卤代酸的谷胱甘肽依赖性氧化或共轭反应。对人类受试者反复给予二氯乙酸会增加其血浆消除半衰期，而给予二氯乙酸的大鼠体内谷胱甘肽转移酶ζ的活性会降低。本文所述研究的目的是探究二氯乙酸诱导谷胱甘肽转移酶ζ活性降低的动力学和机制。肝胞质溶胶中依赖二氯乙酸的谷胱甘肽转移酶ζ失活的速率常数（k(inact)）顺序如下：大鼠＞小鼠＞人类；所研究的物种中二氯乙酸的半数最大抑制浓度（K(inact)）没有差异。与二氯乙酸相反，氯氟乙酸对小鼠肝脏谷胱甘肽转移酶ζ活性的失活作用要小得多。此外，添加N-乙酰-L-半胱氨酸或氰化钾并不能完全阻断二氯乙酸诱导的谷胱甘肽转移酶ζ失活。二氯乙酸诱导重组人谷胱甘肽转移酶ζ（hGSTZ1-1）的四种多态变体失活的k(inact)值顺序如下：变体1a-1a＜1b-1b≈1c-1c≈1d-1d。二氯乙酸诱导的hGSTZ1-1失活是不可逆的。已证实[1-(14)C]二氯乙酸和[(35)S]谷胱甘肽的放射性与重组hGSTZ1c-1c结合，表明该蛋白发生了共价修饰。这些结果表明，二氯乙酸是谷胱甘肽转移酶ζ的一种基于机制的失活剂，并被生物转化为亲电代谢物，这些代谢物共价修饰并因此使该酶失活。
