Binding of isoquinoline alkaloids berberine, palmatine and coralyne to hemoglobin: structural and thermodynamic characterization studies

Abstract

Berberine, palmatine and coralyne, the isoquinoline alkaloids distributed in many botanical families, are extensively investigated due to their potential therapeutic actions and clinical utilities. In this work, their binding characteristics to hemoglobin (Hb) were studied by UV-vis absorption spectroscopy, fluorescence spectroscopy, circular dichroism spectroscopy, isothermal calorimetric titration and differential scanning calorimetric techniques. The results indicated that all the three alkaloids caused strong fluorescence quenching of Hb by the static quenching mechanism, but with differing quenching efficiencies. There was a single binding site on Hb for these alkaloids. According to the theory of Förster resonance energy transfer, the binding distances between β-Trp37 of Hb and berberine, palmatine and coralyne were evaluated to be 2.78 nm, 2.64 nm and 3.29 nm, respectively. The result of synchronous fluorescence, circular dichroism and 3D fluorescence revealed that the polarity around Trp residues experienced a significant increase in the presence of alkaloids. The binding was favoured by enthalpy and entropy changes. Results of circular dichroism, 3D and synchronous fluorescence studies confirmed that the binding of the alkaloids significantly changed the secondary structure of Hb. The studies revealed that berberine and palmatine bound to a site near to the α1β2 interface on Hb different than coralyne but the affinity of coralyne was one order higher than that of berberine and palmatine.

Biological assessment of neonicotinoids imidacloprid and its major metabolites for potentially human health using globular proteins as a model

“…The results indicate Stern-Volmer quenching constants K SV are oppositely correlated with temperature and the values of k q are much bigger than the maximum diffusion-controlled collisional quenching constant ($10 10 M À1 s À1 ), inferring the fluorescence quenching mechanism of proteins by imidacloprid is largely static type, as higher temperature will normally incur the dissociation of weakly bound complexes, and smaller amounts of static quenching [47,48].…”

Exploration of binding of bisphenol A and its analogues with calf thymus DNA by optical spectroscopic and molecular docking methods

“…According to these theory calculations, the electron transfer from DNA bases to BPA and its analogues occurred, which might be one main reason for the fluorescence quenching of BPA and its analogues induced by ctDNA. When BPA and its analogues interact with the bases pairs of ctDNA, electrons would be transferred from the bases to the excited state of them, which could result in quenching of the fluorescence intensity of them [48]. In addition, the positive values of BPAP and BHPF with DNA bases are larger than that of BPA, DPA and BPAP, implying that the electron transport ability enhanced with the increasing number of aromatic rings.…”

“…c (BPA) = c (DPA) = c (BPAF) = c (BPAP) = 5.0 Â 10 À5 mol L À1 , c (BHPF) = 2.5 Â 10 À5 mol L À1 ; the concentration of ctDNA (B, D, F, H, J): 18.0 Â 10 À5 mol L À1 .of the fluorescence functional groups[47,48]. The three-dimensional fluorescence spectra of bisphenol compounds in the absence and presence of ctDNA are shown inFig.…”

Binding of the alkaloid aristololactam-β-D-glucoside and daunomycin to human hemoglobin: spectroscopy and calorimetry studies

“…The 208 nm band corresponds to π-π* transition of the α-helix and the 222 nm band is due to n-π* transition for both the α-helix and random coil conformations (Woody, 1995;Woody, 1996). From the far-UV CD spectral data the α-helical content of Hb was calculated according to the equation given in the literature (Hazra, Hossain, Suresh Kumar, 2013) and the value obtained was 39%, which was in full agreement with the previous reports (Woody, 1995;Woody, 1996;Chen, Yang, Martinez, 1972). As DAN was titrated to the Hb sample, the molar ellipticity of Hb displayed a gradual reduction with the occurrence of a sharp isodichroic point at 203 nm ( Figure 6A) Figure 6B) has one positive maximum centered at 413 nm and a negative minimum around 395 nm (Chen, Yang, Martinez, 1972).…”