用荧光光度法及紫外分光光度法研究了生理条件下金属离子Ca2+、Cu2+和Zn2+对叶酸(FA)与牛血清白蛋白(BSA)相互作用的影响。结果表明:叶酸及金属离子均导致BSA的内源荧光猝灭,根据Stern-Volmer方程得到的荧光猝灭常数,可判断猝灭机制均为静态猝灭。由计算得到的热力学参数熵变ΔS和Gibbs自由能ΔG得出:推断无金属离子存在时,FA与BSA之间的作用力为静电作用力;在Ca2+的存在下,FA对BSA的作用力主要为氢键与范德华力;Cu2+和Zn2+存在下,FA对BSA的作用力主要为疏水作用力。3种金属离子的参与都使得FA与BSA结合作用的表观结合常数发生了的变化,但结合位点数仍维持在1左右。

The effect of metal ions (i.e., Ca2+, Cu2+ and Zn2+) on the interaction between folic acid (FA) and bovine serum albumin (BSA) under physiological condition was studied by fluorospectrophotometry and UV-spectrophotometry. It was shown that the inherent fluorescence of BSA was quenched in the presence of either the folic acid or the 3 metal ions. Judging from the fluorescence quenching constants obtained by Stern-Volmer equation, fluorescence quenching of BSA by FA, Ca2+, Cu2+ and Zn2+ were attributed to static quenching. Values of thermodynamic parameters ΔS and ΔG were calculated and based on these results, the binding force between FA and BSA was recognized to be electrostatic attraction in the absence of metal ions; while in the presence of Ca2+, the main binding force between FA and BSA was hydrogen bond and Van der Waals force; and in the presence of Cu2+or Zn2+, the binding force between FA and BSA was due to the hydrophobic effect. The binding constants between FA and BSA were changed in the presence of metal ions, but number of binding sites was still kept at around 1.