Surfactants have a considerable potential for inhibiting horseradish peroxidase (HRP) activity; yet, more research is needed to understand the inhibition mechanism to allow for choosing the suitable surfactant candidate as inhibitor. In this study, three traditional surfactants, sodium dodecyl sulfate (SDS), N-dodecyltrimethyl ammonium bromide (DTAB) and N-dodecyldimethyl (3-sulfopropyl) ammonium hydroxide (SB3-12), that share the same (C₁₂) hydrophobic tail but possess different charged head groups, were taken as model surfactant inhibitors, and the enzymatic activity of HRP was assessed in these surfactant solutions. The activity of HRP was inhibited by both anionic SDS and cationic DTAB at dilute concentration even below their critical micelle concentration (cmc), and the electrostatic interaction of the ionic surfactants with some amino residues of HRP was mainly responsible for the inhibition of activity. HRP in a dilute solution of SB3-12, with the latter's concentration being below its cmc, retained a high level of enzymatic activity; but, at concentrations above the cmc of SB3-12, HRP was inhibited owing to the synergetic interaction of the SB3-12 micelle with HRP. Results from circular dichroism (CD) and intrinsic fluorescence spectroscopic analyses of HRP showed the unfolding of the tertiary structure around HRP's heme active site played a critical role in the inhibition, whereas the changes of HRP in the secondary structure and the tertiary structure near its tryptophan residue (Trp117) induced by these surfactants were minor for the inhibition. Based on the experimental results, a relationship between conformation and activity for HRP was suggested.

中文翻译：

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通过表面活性剂溶液的构象变化抑制辣根过氧化物酶活性

表面活性剂具有相当大的抑制辣根过氧化物酶 (HRP) 活性的潜力；然而，需要更多的研究来了解抑制机制，以便选择合适的表面活性剂候选物作为抑制剂。在这项研究中，三种传统的表面活性剂，十二烷基硫酸钠 (SDS)、N-十二烷基三甲基溴化铵 (DTAB) 和N-十二烷基二甲基 (3-磺丙基) 氢氧化铵 (SB3-12)，它们具有相同的 (C ₁₂) 疏水尾但具有不同的带电头部基团，作为模型表面活性剂抑制剂，并在这些表面活性剂溶液中评估 HRP 的酶活性。阴离子 SDS 和阳离子 DTAB 在稀释浓度甚至低于其临界胶束浓度 (cmc) 时都抑制 HRP 的活性，离子表面活性剂与 HRP 的一些氨基残基的静电相互作用是抑制活性的主要原因。HRP 在 SB3-12 的稀溶液中，后者的浓度低于其 cmc，保留了高水平的酶活性；但是，在浓度高于 SB3-12 的 cmc 时，由于 SB3-12 胶束与 HRP 的协同相互作用，HRP 受到抑制。HRP的圆二色性（CD）和固有荧光光谱分析结果表明，HRP血红素活性位点周围三级结构的展开在抑制中起关键作用，而HRP二级结构和色氨酸附近三级结构的变化这些表面活性剂诱导的残留物（Trp117）对抑制作用很小。根据实验结果，提出了 HRP 的构象和活性之间的关系。