Interaction of malachite green with bovine serum albumin: determination of the binding mechanism and binding site by spectroscopic methods.

Background and purpose: Monoamine oxidase inhibitors (MAOI) are known to cause serotonin toxicity (ST) when administered with selective serotonin reuptake inhibitors (SSRI). Methylene blue (methylthionium chloride, MB), a redox dye in clinical use, has been reported to precipitate ST in patients using SSRI. MB was assessed for MAO inhibition and so for its potential to precipitate ST. Experimental approach: Inhibition of purified human MAO was quantified using kinetic assays and visible spectral changes to study the interactions of MB with MAO A. Key results: MB was a potent (tight binding) inhibitor for MAO A. It also inhibited MAO B but at much higher concentration. Interactions of MB with the active site of MAO A were confirmed by its action both as an oxidising substrate and as a one-electron reductant. Conclusions and implications: MB is a potent reversible inhibitor of MAO A with implications for gut uptake of amines when administered orally. At concentrations reported in the literature after intravenous administration, MAO B would be partially inhibited but MAO A would be completely inhibited. This inhibition of MAO A would be expected to lead to perturbations of 5-hydroxytryptamine metabolism and hence account for ST occurring when administered to patients on SSRI treatment. British Journal of Pharmacology (2007) 152, 946–951; doi:10.1038/sj.bjp.0707430; published online 27 August 2007

Methylene blue and serotonin toxicity: inhibition of monoamine oxidase A (MAO A) confirms a theoretical prediction

The interaction of Bovine Serum Albumin (BSA) with limonene has been studied by UV-visible spectroscopy, fluorescence spectroscopy and molecular docking, and its effects on protein conformation, topology and stability were determined by Circular Dichroism (CD), Dynamic Light Scattering (DLS) and Differential Scanning Calorimetry (DSC). A gradual decrease in Stern–Volmer quenching constants with the increase in temperature showed the static mode of fluorescence quenching. The obtained binding constant (Kb) was ∼104 M−1. The temperature dependent Kb, Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) changes were calculated, which revealed that the reaction is spontaneous and exothermic. The UV-visible spectra showed a change in the peaks within the aromatic region indicating hydrophobic interactions with Trp, Tyr and Phe in the protein. Moreover, limonene induced an increase in α-helical contents probably on the cost of random coils or/and β-sheets of BSA, as observed from the far-UV CD spectra. The topology of BSA in the presence of limonene was slightly altered, as obtained from DLS results. The stability was also enhanced as revealed through thermal denaturation study by DSC and CD. Molecular docking study depicted that limonene fits into the hydrophobic pocket close to Sudlow site I in domain IIA of BSA. The present study will be helpful in understanding the binding mechanism of limonene and associated stability and conformational changes.

Elucidating the interaction of limonene with bovine serum albumin: a multi-technique approach

The interactions of 3-carboxyphenoxathiin with Bovine Serum Albumin (BSA) and Human Serum Albumin (HSA) have been studied by fluorescence and circular dichroism spectroscopy. The binding of 3-carboxyphenoxathiin quenches the BSA and HSA fluorescence, revealing a 1:1 interaction with a binding constant of about 10(5) M(-1). In addition, according to the synchronous fluorescence spectra of BSA and HSA in presence of 3-carboxyphenoxathiin, the tryptophan residues of the proteins are most perturbed by the binding process. Finally, the distance between the acceptor, 3-carboxyphenoxathiin, and the donor, BSA or HSA, was estimated on the basis of the Forster resonance energy transfer (FRET). The fluorescence results are correlated with those obtained from the circular dichroism spectra, which reveal the change of the albumin conformation during the interaction process.

https://www.mdpi.com/1420-3049/15/6/3905/pdf?view=inline

Bovine and human serum albumin interactions with 3-carboxyphenoxathiin studied by fluorescence and circular dichroism spectroscopy.

Characterization of the baicalein–bovine serum albumin complex without or with Cu2+or Fe3+ by spectroscopic approaches

The interaction between methylene blue (MB) and bovine serum albumin (BSA) was investigated by fluorescence and UV–vis absorbance spectroscopy. In the mechanism discussion, it was proved that the fluorescence quenching of BSA by MB is mainly a result of the formation of MB–BSA complex and electrostatic interactions play an important role to stabilize the complex. The Stern–Volmer quenching constant K SV and corresponding thermodynamic parameters Δ H , Δ G , and Δ S were calculated. The distance r between donor (BSA) and acceptor (MB) was obtained according to fluorescence resonance energy transfer (FRET). The effect of MB on the conformation of BSA has been analyzed by means of UV–vis absorbance spectra and synchronous fluorescence spectroscopy.

Jia-Xin Dong

Papers

Spectroscopic studies on the interaction between methylene blue and bovine serum albumin

Fluorometric investigation of the interaction between methylene blue and human serum albumin

Interaction of loratadine with serum albumins studied by fluorescence quenching method.

A solution-reaction isoperibol calorimeter and standard molar enthalpies of formation of Ln(hq)2Ac (Ln = La, Pr)

Spectroscopic studies on the interaction between 3,4,5-trimethoxybenzoic acid and bovine serum albumin