We conclude that the modified Hb in cigarette smokers may further enhance the oxidative insult within the cell.

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Linezolid, one of the reserve antibiotic of oxazolidinone class has wide range of antimicrobial activity. Here we have conducted a fundamental study concerning the dynamics of its interaction with bovine serum albumin (BSA), and the post binding modification of the later by employing different spectroscopic (absorption, fluorescence and circular dichroism (CD) spectroscopy) and molecular docking tools. Gradual quenching of the tryptophan (Trp) fluorescence upon addition of linezolid to BSA confirms their interaction. Analysis of fluorescence quenching at different temperature indicates that the interaction is made by static complex formation and the BSA has one binding site for the drug. The negative Gibbs energy change (ΔG), and positive values of enthalpy change (ΔH) and entropy change (ΔS) strongly suggest that it is an entropy driven spontaneous and endothermic reaction. The reaction involves hydrophobic pocket of the protein, which is further stabilized by hydrogen bonding and electrostatic interactions as evidenced from 8-anilino-1-napthalene sulfonic acid, sucrose and NaCl binding studies. These findings also support the molecular docking study using AutoDock 4.2. The influence of this interaction on the secondary structure of the protein is negligible as evidenced by CD spectroscopy. So, from these findings, we conclude that linezolid interacts with BSA in 1:1 ratio through hydrophobic, hydrogen bonding and ionic interactions, and this may not affect the secondary structure of the protein.

Etoricoxib, widely used for the treatment of osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, and related conditions has ample affinity to bind with globular proteins. Here, the molecular interaction between purified human hemoglobin (HHb), a major heme protein and etoricoxib, a cyclooxygenase-2 inhibitor was studied by various spectroscopic, calorimetric, and molecular modeling techniques. The binding affected hypochromic changes in the Soret band of hemoglobin (Hb) and induced remarkable quenching of the intrinsic fluorescence property of protein molecules. Synchronous fluorescence studies revealed alterations in tryptophan (Trp) and tyrosine (Tyr) microenvironments of HHb molecule in presence of etoricoxib. Flouremetric and isothermal titration calorimetric studies suggested two binding sites in HHb for etoricoxib at three different temperatures (298.15, 303.15, and 310.15 K). Negative values of Gibbs energy change (ΔG) and enthalpy change (ΔH) strongly suggest that it is spontaneous and exothermic reaction, mainly stabilized by hydrogen bonding as evidenced by sucrose binding assay. These findings support our in silico molecular docking study, which specified the binding site and the non-covalent interactions involved in the association. Moreover, the interaction impacts on structural integrity and functional aspects of HHb as confirmed by decreased α helicity, increased free iron release, increased rate of co-oxidation, and decreased rate of esterase activity. Overall, these studies conclude that etoricoxib leads to a remarkable alteration in the conformational aspects of binding to HHb. Communicated by Ramaswamy H. Sarma.

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