Danielson U H, Mannervik B
Biochem J. 1985 Oct 15;231(2):263-7. doi: 10.1042/bj2310263.
The steady-state kinetics of the dimeric glutathione transferases deviate from Michaelis-Menten kinetics, but have hyperbolic binding isotherms for substrates and products of the enzymic reaction. The possibility of subunit interactions during catalysis as an explanation for the rate behaviour was investigated by use of rat isoenzymes composed of subunits 1, 2, 3 and 4, which have distinct substrate specificities. The kinetic parameter kcat./Km was determined with 1-chloro-2,4-dinitrobenzene, 4-hydroxyalk-2-enals, ethacrynic acid and trans-4-phenylbut-3-en-2-one as electrophilic substrates for six isoenzymes: rat glutathione transferases 1-1, 1-2, 2-2, 3-3, 3-4 and 4-4. It was found that the kcat./Km values for the heterodimeric transferases 1-2 and 3-4 could be predicted from the kcat./Km values of the corresponding homodimers. Likewise, the initial velocities determined with transferases 3-3, 3-4 and 4-4 at different degrees of saturation with glutathione and 1-chloro-2,4-dinitrobenzene demonstrated that the kinetic properties of the subunits are additive. These results show that the subunits of glutathione transferase are kinetically independent.
二聚体谷胱甘肽转移酶的稳态动力学偏离米氏动力学，但对酶促反应的底物和产物具有双曲线结合等温线。通过使用由具有不同底物特异性的亚基1、2、3和4组成的大鼠同工酶，研究了催化过程中亚基相互作用作为速率行为解释的可能性。以1-氯-2,4-二硝基苯、4-羟基链-2-烯醛、依他尼酸和反式-4-苯基丁-3-烯-2-酮作为六种同工酶（大鼠谷胱甘肽转移酶1-1、1-2、2-2、3-3、3-4和4-4）的亲电底物，测定了动力学参数kcat./Km。发现异二聚体转移酶1-2和3-4的kcat./Km值可以从相应同二聚体的kcat./Km值预测。同样，用转移酶3-3、3-4和4-4在谷胱甘肽和1-氯-2,4-二硝基苯不同饱和度下测定的初始速度表明，亚基的动力学性质是可加的。这些结果表明谷胱甘肽转移酶的亚基在动力学上是独立的。
