Herein, we report a comprehensive study on the interaction of three protomeric forms of the antibacterial drug norfloxacin (nfx) with the enzymatic protein human lysozyme (lyz). Norfloxacin, having the option for two-stage acid–base equilibria, converts from cationic (nfx⁺) to zwitterionic (nfx^±) form, followed by an anionic (nfx^–) species, with increasing pH. Among these protomeric forms, lysozyme binds nfx^± most robustly, whereas nfx^– has a weak association and nfx⁺ does not show any interaction. In lysozyme, the location of the drug was ascertained by competitive binding assay with 8-anilino-1-naphthalenesulfonate, and this was further examined with molecular docking simulation. The binding process was found to be primarily governed by hydrogen bonding and van der Waals interactions. The study has further revealed that preferential binding of nfx^± by the protein over nfx^– led to a switchover of nfx^– to nfx^±; and the resulting increased population of nfx^± over the other is beneficial for the pharmacological activity of the drug in terms of its accumulation in the target bacterial cells. The present study accomplishes two important objectives. It holds significance regarding the differential interaction of multiprotomeric drugs with biomolecules, such as proteins, enzymes, lipid membranes, etc., and also on such biomolecule-assisted alteration of the acid–base equilibrium and consequent bioavailability of the drug. The findings are useful from the viewpoints of dispensation, distribution, and metabolism of any prototropic drug in living systems as they encounter several biomolecules in vivo. Another importance of this work stems from the study of comparative binding responses of lysozyme toward a drug existing in multiple forms depending on its protonation states or some other chemical processes.

中文翻译：

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在溶菌酶口袋中安置的诺罗沙星的不同质子形式的命运的对策方案：蛋白质内部的非静电相互作用在客体质子平衡中的控制作用。

在这里，我们报告了抗菌药物诺氟沙星（nfx）的三种原型形式与酶蛋白人溶菌酶（lyz）相互作用的综合研究。诺氟沙星具有两步酸碱平衡的选项，随着pH值的增加，它会从阳离子形式（nfx ⁺）转换为两性离子形式（nfx ^±），然后是阴离子形式（nfx ^–）。在这些protomeric形式，溶菌酶结合NFX ^±最稳健，而NFX ^-具有弱关联和NFX ⁺没有显示任何互动。在溶菌酶中，通过与8-苯胺基-1-萘磺酸盐的竞争性结合测定法确定了药物的位置，并通过分子对接模拟对其进行了进一步检查。发现结合过程主要受氢键和范德华相互作用的支配。该研究进一步揭示了优惠NFX结合^±通过蛋白质过度NFX ^-导致NFX的切换^-到NFX ^± ; 并导致人口增加nfx ^±另一方面，就其在靶细菌细胞中的积累而言，对药物的药理活性是有益的。本研究完成了两个重要目标。它对多蛋白药物与生物分子（例如蛋白质，酶，脂质膜等）的差异相互作用具有重要意义，而且在这种生物分子辅助的酸碱平衡变化和随之而来的药物生物利用度方面也具有重要意义。从任何质子传递药物在生命系统中的分布，分布和代谢的角度来看，这些发现都是有用的，因为它们在体内会遇到几种生物分子。这项工作的另一个重要性源于对溶菌酶对以质子化状态或某些其他化学过程存在的多种形式存在的药物的相对结合反应的研究。