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• Fluorescence,3D,Syn,UV–vis,FT-IR,Mol.Docking affirmed BSA-LVG interaction. • BSA intrinsic fluorescence was quenched by LVG via static mechanism. • LVG binding altered BSA native conformation. • Site probing, Mol.Docking revealed LVG at interface of BSA subdomains IIA & IIIA. • ASC, SAL suppressed BSA binding affinity for levonorgestrel. Serum proteins generally help to transport and distribute drug molecules within the body. In this study, the binding characteristics of bovine serum albumin (BSA) with levonorgestrel (LVG), an emergency contraceptive pill, and the influences of ascorbic acid (ASC) and salicylic acid (SAL) on the binding behaviour and protein structure were elucidated using multi-spectroscopic techniques and molecular docking. The results showed that levonorgestrel decreased BSA intrinsic fluorescence via static quenching mechanism. Binding constant (K a) values for BSA-LVG complexes were 103 to 104 M-1, indicating their high stabilities. Site probing/docking analysis indicated LVG bound between BSA subdomains IIA and IIIA. UV–visible absorption, Fourier Transform-Infrared and 3D fluorescence spectroscopies affirmed LVG-induced changes in BSA structure, especially in α-helix and β-sheet contents. ASC and SAL influenced BSA conformation for LVG binding and reduced the K a values by 3.37 and 5.43-folds, respectively. LVG altered the microenvironments of tyrosine residues, interacted with Arg-217, Lys-221, Val-292, Glu-443 etc. within the binding domains. The process was spontaneous (ΔG<0), entropy driven (TΔS>ΔH) and involved van der Waals forces and hydrogen bonding. The findings of the study offered details on the binding interaction between BSA and LVG, and also indicated that prior intake of ASC or SAL could suppress the binding affinity of BSA for levonorgestrel. [Display omitted] [ABSTRACT FROM AUTHOR]

The present study investigated the antioxidant and in vitro antidiabetic capacities of Justicia carnea aqueous leaf extract (JCAE) using α-amylase inhibition model. α-Amylase binding-interaction with JCAE was also investigated using fluorescence spectroscopy and molecular docking. Phytochemical screening and Gas Chromatography-Mass Spectrometry (GC–MS) analysis indicated presence of bioactive compounds. Phenolic (132 mg GAE/g) and flavonoid contents (31.08 mg CE/g) were high. JCAE exhibited high antioxidant capacity and effectively inhibited α-amylase activity (IC 50 , 671.43 ± 1.88 μg/mL), though lesser than acarbose effect (IC 50 , 108.91 ± 0.61 μg/mL). α-Amylase intrinsic fluorescence was quenched in the presence of JCAE. Ultraviolet-visible and FT-IR spectroscopies affirmed mild changes in α-amylase conformation. Synchronous fluorescence analysis indicated alterations in the microenvironments of tryptophan residues near α-amylase active site. Molecular docking affirmed non-polar interactions of compounds 6 and 7 in JCAE with Asp-197 and Trp-58 residues of α-amylase, respectively. Overall, JCAE indicated potential to prevent postprandial hyperglycemia by slowing down carbohydrate hydrolysis. Unlabelled Image • UV–vis, FT-IR and fluorescence provide evidence of α-amylase interaction with JCAE. • JCAE inhibited α-amylase activity and quenched α-amylase intrinsic fluorescence. • Microenvironments of tryptophan residues near α-amylase active site were altered. • Compounds 6 and 7 in JCAE showed highest binding affinities to α-amylase. • JCAE could be a potential source of novel α-amylase inhibitors. [ABSTRACT FROM AUTHOR]