Schmidt Anne-Christine, Neustadt Madlen, Otto Matthias
TU Bergakademie Freiberg, Faculty of Chemistry and Physics, Institute of Analytical Chemistry, Freiberg, Germany.
J Mass Spectrom. 2007 Jun;42(6):771-80. doi: 10.1002/jms.1212.
An attempt was made to quantitatively describe the binding of phenylarsenic species to thiol-containing biomolecules using electrospray ionization mass spectrometry (ESI-MS). The extent of the reactions of phenylarsine oxide (PAO) with the peptides glutathione and isotocin (ITC) and with the protein thioredoxin resulting in covalent As--S bonds were quantified by deriving the dependence of the corresponding ion signal intensities on the concentration of the reaction products. Problems complicating a quantitative evaluation of the mass spectra, such as signal suppression effects, were critically evaluated. Equilibrium constants for condensation reactions as well as formation constants for noncovalent associations were calculated by means of ESI-MS signal intensities. The comparison of the reaction of PAO with different thiol reactants revealed the highest binding affinity for ITC followed by thioredoxin and a lower affinity to glutathione. Possibly, the intramolecular formation of RS-As(C(6)H(5))-SR occurring in case of ITC and thioredoxin is favored over the intermolecular product involving two molecules glutathione even though the molecular mass of glutathione (307 g mol(-1)) is much smaller than that of ITC (966 g mol(-1)) and thioredoxin (11 688 g mol(-1)). A similar binding affinity for trivalent (K approximately 1.6 x 10(-3) l micromol(-1)) and pentavalent (K approximately 1.6 x 10(-3) and 1.0 x 10(-3) l micromol(-1)) arsenic species was found for the formation of a noncovalent complex of glutathione with different phenylarsenic compounds.
人们尝试使用电喷雾电离质谱法（ESI-MS）对苯基砷化合物与含硫醇生物分子的结合进行定量描述。通过推导相应离子信号强度对反应产物浓度的依赖性，对苯基氧化砷（PAO）与肽类谷胱甘肽和异缩宫素（ITC）以及与蛋白质硫氧还蛋白反应生成共价As—S键的反应程度进行了定量分析。对质谱定量评估中存在的复杂问题，如信号抑制效应，进行了严格评估。通过ESI-MS信号强度计算了缩合反应的平衡常数以及非共价缔合的形成常数。PAO与不同硫醇反应物反应的比较表明，其对ITC的结合亲和力最高，其次是硫氧还蛋白，对谷胱甘肽的亲和力较低。尽管谷胱甘肽的分子量（307 g·mol⁻¹）远小于ITC（966 g·mol⁻¹）和硫氧还蛋白（11688 g·mol⁻¹），但在ITC和硫氧还蛋白的情况下，分子内形成RS-As(C₆H₅)-SR可能比涉及两个谷胱甘肽分子的分子间产物更受青睐。对于谷胱甘肽与不同苯基砷化合物形成非共价复合物，发现三价砷（K约为1.6×10⁻³ l·μmol⁻¹）和五价砷（K约为1.6×10⁻³和1.0×10⁻³ l·μmol⁻¹）具有相似的结合亲和力。
