Andersson C, Söderström M, Mannervik B
Department of Biochemistry, Arrhenius Laboratory, University of Stockholm, Sweden.
Biochem J. 1988 Feb 1;249(3):819-23. doi: 10.1042/bj2490819.
Mouse liver microsomal glutathione transferase was purified in an N-ethylmaleimide-activated as well as an unactivated form. The enzyme had a molecular mass of 17 kDa and a pI of 8.8. It showed cross-reactivity with antibodies raised against rat liver microsomal glutathione transferase, but not with any of the available antisera raised against cytosolic glutathione transferases. The fully N-ethylmaleimide-activated enzyme could be further activated 1.5-fold by inclusion of 1 microM-bromosulphophthalein in the assay system. The latter effect was reversible, which was not the case for the N-ethylmaleimide activation. At 20 microM-bromosulphophthalein the activated microsomal glutathione transferase was strongly inhibited, while the unactivated form was activated 2.5-fold. Inhibitors of the microsomal glutathione transferase from mouse liver showed either about the same I50 values for the activated and the unactivated form of the enzyme, or significantly lower I50 values for the activated form compared with the unactivated form. The low I50 values and the steep slope of the activity-versus-inhibitor-concentration curves for the latter group of inhibitors tested on the activated enzyme indicate a co-operative effect involving conversion of activated enzyme into the unactivated form, as well as conventional inhibition of the enzyme.
小鼠肝脏微粒体谷胱甘肽转移酶以N - 乙基马来酰亚胺激活形式和未激活形式进行了纯化。该酶的分子量为17 kDa，pI为8.8。它与针对大鼠肝脏微粒体谷胱甘肽转移酶产生的抗体有交叉反应，但与针对胞质谷胱甘肽转移酶的任何现有抗血清均无交叉反应。在测定系统中加入1 microM - 溴磺酞可使完全N - 乙基马来酰亚胺激活的酶进一步激活1.5倍。后一种效应是可逆的，而N - 乙基马来酰亚胺激活则不然。在20 microM - 溴磺酞时，激活的微粒体谷胱甘肽转移酶受到强烈抑制，而未激活形式则被激活2.5倍。小鼠肝脏微粒体谷胱甘肽转移酶的抑制剂对该酶的激活形式和未激活形式显示出大致相同的I50值，或者与未激活形式相比，激活形式的I50值显著更低。在激活酶上测试的后一组抑制剂的低I50值和活性与抑制剂浓度曲线的陡坡表明存在一种协同效应，涉及激活酶向未激活形式的转化以及对该酶的常规抑制。
