稀土离子对烟草RuBPcase的抑制作用

Effects of Ln^(3+) on Inhibition of Tobacco RuBPcase

采用硫酸铵沉淀和SephadexG 2 0 0柱层析分离纯化出烟草RuBPcase ( 1,5 二磷酸核酮糖羧化酶 ) ,并测定了稀土元素离子对酶活性抑制效果。在RuBPcase催化CO2 固定的反应体系中 ,随着稀土元素离子浓度的增加 ,该酶对Mg2 + 的最大反应速度 (vmax)不变 ,米氏常数 (km)变大 ,并带有一个抑制剂常数 (ki)的典型竞争性抑制。La3+ ,Ce3+ ,Gd3+ 的ki 分别为 :2 6 3,34 3,2 0 0 (mol·L- 1 ,3种离子与Mg2 + 对RuBPcase竞争能力的大小顺序为La3+ >Ce3+ Gd3+ 。

The tobacco RuBPcase was purified by the method of (NH 4) 2SO 4 precipitation and Sephadex G 200 column chromatography. The effects of rare earth element ions on inhibition of RuBPcase activity were studied. The result reveals that the v max of RuBPcase is unchanged, but its k m increases with inhibitor content k i when increasing the concentration of rare earth element ion in enzymatic reaction. It indicates that the inhibition of rare earth element ion is a typical competitive inhibition with Mg 2+ . The k i of La 3+ , Ce 3+ and Gd 3+ is 26 3, 34 3 and 200 μmol·L -1 , respectively. Their inhibitory action on RuBPcase is in the order of La 3+ >Ce 3+ Gd 3+ .