Department of Physical Chemistry and Department of Applied Mechanics and Project Engineering, University of Castilla-La Mancha, Campus Universitario, E-02071-Albacete, Spain.
Chem Res Toxicol. 2009 Nov;22(11):1841-50. doi: 10.1021/tx9002512.
Oxidation of acetaminophen by human methemoglobin in the presence of H(2)O(2) has been kinetically studied in the present paper. The drug showed a protective effect against the H(2)O(2)-induced irreversible inactivation of the protein, thus indicating the competition among both ligands, H(2)O(2) and acetaminophen for the protein. The stoichiometry of the reaction is variable and depends on relative initial concentrations of H(2)O(2) and the drug owing to their competitive behavior. In addition and unexpectedly, the protein exhibits non Michaelian kinetics against both acetaminophen and H(2)O(2) under steady-state conditions and shows negative co-operativity with Hill coefficients in the 0.3-0.7 range. Therefore, these data were compared to those obtained with myoglobin under similar experimental conditions, and the same results were observed. This led us to propose a mechanism for the peroxidase-like activity of hemoglobin, which accounts for the experimental results obtained herein. The steady-state rate equation for this mechanism has been obtained and is also consistent with the experimental data, thus indicating the goodness of the model proposed herein. The results presented in this work provide new insights into the oxidation mechanism of acetaminophen.
本文对人高铁血红蛋白在 H₂O₂存在下氧化对乙酰氨基酚的动力学进行了研究。该药物对 H₂O₂诱导的蛋白质不可逆失活表现出保护作用，表明两种配体（H₂O₂和对乙酰氨基酚）与蛋白质竞争。反应的化学计量是可变的，并且取决于相对初始浓度的 H₂O₂和药物，这是由于它们的竞争行为。此外，出人意料的是，在稳态条件下，该蛋白质对乙酰氨基酚和 H₂O₂表现出非米氏动力学，并显示出 0.3-0.7 范围内的负协同作用和 Hill 系数。因此，将这些数据与在类似实验条件下获得的肌红蛋白的数据进行比较，观察到了相同的结果。这使我们提出了血红蛋白过氧化物酶样活性的机制，该机制解释了本文获得的实验结果。已经获得了该机制的稳态速率方程，并且与实验数据一致，从而表明本文提出的模型的良好性。本工作的结果为对乙酰氨基酚的氧化机制提供了新的见解。
