Ricci G, Del Boccio G, Pennelli A, Aceto A, Whitehead E P, Federici G
Institute of Biochemical Sciences, University of Chieti D'Annunzio, Italy.
J Biol Chem. 1989 Apr 5;264(10):5462-7.
Glutathione transferase (EC 2.5.1.18) from horse erythrocytes has been purified and some molecular and kinetic properties have been investigated. It appears to be a dimeric protein composed of subunits of about 23 kDa, indistinguishable either in sodium dodecyl sulfate or in urea electrophoresis. Amino acid composition, substrate specificities, sensitivity to inhibitors, CD spectra, and immunological studies provide evidence that the horse enzyme is related to the pi class transferases. This enzyme has only two reactive thiol groups/dimer whose integrity appears to be essential for the activity. A peculiar feature of these protein thiol groups is that they react nonidentically with a number of thiol blocking reagents, i.e. iodacetamide, bromopyruvate, N-ethylmaleimide, and 1-chloro-2,4-dinitrobenzene. Also many disulfides react with one thiol group 5- to 10-fold more rapidly than with the other. The two mixed disulfides so formed also have different rates of reactivation by dithiothreitol. All the structural and kinetic data reported in this paper indicate a nonsymmetrical association of two identical subunits, or alternatively heterodimeric structure with subunits of very similar charge and size.
已对马红细胞中的谷胱甘肽转移酶（EC 2.5.1.18）进行了纯化，并研究了其一些分子和动力学特性。它似乎是一种由约23 kDa亚基组成的二聚体蛋白，在十二烷基硫酸钠或尿素电泳中无法区分。氨基酸组成、底物特异性、对抑制剂的敏感性、圆二色光谱和免疫学研究提供了证据，表明马酶与π类转移酶有关。该酶每个二聚体只有两个反应性巯基，其完整性似乎对活性至关重要。这些蛋白质巯基的一个独特特征是它们与许多巯基阻断试剂（即碘乙酰胺、溴丙酮酸、N-乙基马来酰亚胺和1-氯-2,4-二硝基苯）的反应不同。许多二硫键与一个巯基的反应速度也比与另一个巯基快5至10倍。如此形成的两种混合二硫键被二硫苏糖醇再活化的速率也不同。本文报道的所有结构和动力学数据表明，两个相同亚基呈非对称缔合，或者是具有非常相似电荷和大小的亚基组成的异二聚体结构。
