微分脉冲极谱法研究稀土离子对乳酸脱氢酶活性的影响

根据前文黄瓜根系伤流液(经La³⁺，Eu³⁺处理)中微量La³⁺，Eu³⁺明显影响氨基酸代谢的结果，用记时电流法研究了稀土对氮同化过程中硝酸还原酶(NR)和谷氨酸脱氢酶(GDH)活性的影响，酶活性的变化以辅酶NADH氧化电流在反应中的衰减速度来表示。用微分脉冲极谱法研究稀土离子对丙酮酸转化为乳酸反应中乳酸脱氢酶(LDH)活性的影响，以反应产物NAD⁺的还原电流的大小表示酶活性的变化。研究结果表明La³⁺在低浓度(<5μmol/L)下对酶活性有微弱的促进作用，其他稀土离子Ce³⁺，Eu³⁺, Dy³⁺，Yb³⁺在浓度稍高时(≥5μmol/L)都显示抑制作用。对比光度法的结果以及反应动力学参数V_max和K_m均证明稀土离子对此体系中LDH活性有抑制作用。

The Study of the Effect of Lanthanide Ions on the LDH Activity by Differential pulse Polarography

Differential-pulse polarography(DPP) was applied to studythe effect of lanthanide ions on the LDH activity in the catalyticalreaction of pyruvate+NADH+H⁺=lactate+NAD⁺, by monitoring DPPreduction current of NAD⁺. In a buffer solution of 0.05 mol/L Tris-HCl(pH7.5)+0.5 mmol/L pyruvate, NAD⁺ exhibits a well-defineddifferential-pulse peak at -0.82V. The peak current is proportionalto NAD⁺ concentration in the range 1-28 micro mol/L. In the assay mixture, low concentration La³⁺ ions(<5 micro mol/L) slightly increase LDHactivity. Other ions Ce³⁺, Eu³⁺, Dy³⁺ andYb³⁺(5 micro mol/L) show inhibitory effects. The data of spectrophotometry and kinetics analysis are in agreement with DPP results.