Binding of 5-(2'-carboxyphenyl)azoquinolin-8-ol to bovine serum albumin: a spectroscopic study

Study on the binding of chloroamphenicol with bovine serum albumin by fluorescence and UV-vis spectroscopy

The binding of chloroamphenicol (CPC) to bovine serum albumin (BSA) at 296 K, 303 K, and 310 K by fluorescence and UV-visible absorption spectroscopy were investigated under imitated physiological conditions. The experimental results showed that the fluorescence quenching mechanism between CPC and BSA was combined quenching (dynamic and static quenching) procedure at low CPC concentration, or a dynamic quenching procedure at high concentrations. The binding constants, binding sites and the corresponding thermodynamic parameters of the interaction system were calculated. According to Förster non-radiation energy transfer theory, the binding distance between CPC and BSA was calculated to be 3.02 nm. Both synchronous fluorescence and FT-IR spectra confirmed the interaction, and indicated the conformational changes of BSA. The effects of some common metal ions Ca(2+), Ni(2+), Mg(2+), Fe(2+), and Cu(2+) on the binding constant between CPC and BSA were examined. Furthermore, we investigated the possible sub-domains on BSA that bind CPC by displacement experiments.

Spectroscopic investigation on the interaction of ICT probe 3-acetyl-4-oxo-6,7-dihydro-12H Indolo-[2,3-a] quinolizine with serum albumins

Interaction of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), a biologically active molecule, with model transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA) have been studied using steady state and picosecond time-resolved fluorescence and fluorescence anisotropy. The polarity dependent intramolecular charge transfer (ICT) process is responsible for the remarkable sensitivity of this biological fluorophore to the protein environments. The CT fluorescence exhibits appreciable hypsochromic shift along with an enhancement in the fluorescence yield, fluorescence anisotropy (r) and fluorescence lifetime upon binding with the proteins. The reduction in the rate of ICT within the hydrophobic interior of albumins leads to an increase in the fluorescence yield and lifetime. Marked increase in the fluorescence anisotropy indicates that the probe molecule is located in a motionally constrained environment within the proteins. Micropolarities in the two proteinous environments have been determined following the polarity sensitivity of the CT emission. Addition of urea to the protein-bound systems leads to a reduction in the fluorescence anisotropy indicating the denaturation of the proteins. Polarity measurements and fluorescence resonance energy transfer (FRET) studies throw light in assessing the location of the fluorophore within the two proteinous media.

Fluorometric investigation of interaction of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine with bovine serum albumin

Interaction of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ) with a model transport protein, bovine serum albumin (BSA), has been studied using steady state fluorescence and fluorescence anisotropy experiments. Upon binding with BSA, the charge transfer (CT) fluorescence exhibits appreciable hypsochromic shift along with an enhancement in the fluorescence intensity. Gradual addition of BSA leads to the marked increase in the fluorescence anisotropy (r). From the high value of fluorescence anisotropy (r=0.30) it is argued that the probe molecule is located in motionally restricted environment of the protein. Addition of urea to the protein bound AODIQ leads to the decrease in fluorescence intensity as well as fluorescence anisotropy (r) indicating the release of AODIQ molecule to the aqueous buffer medium, thus supporting the idea that the protein, in its native form, binds with the probe. The binding constant and free energy change (DeltaG(0)) for the interaction of AODIQ with BSA have been evaluated from relevant fluorescence data. Polarity of the microenvironment has been determined from a comparison of the variation of fluorescence property of the probe in dioxane-water mixture with varying composition.

Photophysical studies on binding of curcumin to bovine serum albumins

The excited-state photophysical properties of curcumin in the presence of bovine serum albumin (BSA) have been studied. The absorption and fluorescence changes in curcumin on binding to BSA have been followed at varying concentrations of either curcumin or BSA to determine the binding constant, which has been found to be approximately 10(4) to 10(5) M(-1). Stopped-flow kinetics studies suggested at least two distinct kinetic steps for the binding of curcumin to BSA. The photophysical properties of the singlet-excited state of the curcumin-BSA complex have also been studied. Whereas the absorption spectrum of curcumin is redshifted, the fluorescence spectrum of curcumin was blueshifted in the presence of BSA. The fluorescence quantum yield of curcumin on complexing with BSA was approximately 0.05. Steady-state fluorescence anisotropy studies showed a significant increase in the anisotropy value of 0.37 in BSA-bound curcumin. The fluorescence decay of the curcumin-BSA complex followed a biexponential decay with fluorescence lifetimes of 413 ps (33%) and 120 ps (67%). On the basis of these complementary results, it has been concluded that curcumin shows very high binding to BSA, probably at the hydrophobic cavities inside the protein.

Photophysical studies on binding of curcumin to bovine serum albumins

The excited-state photophysical properties of curcumin in the presence of bovine serum albumin (BSA) have been studied. The absorption and fluorescence changes in curcumin on binding to BSA have been followed at varying concentrations of either curcumin or BSA to determine the binding constant, which has been found to be approximately 10(4) to 10(5) M(-1). Stopped-flow kinetics studies suggested at least two distinct kinetic steps for the binding of curcumin to BSA. The photophysical properties of the singlet-excited state of the curcumin-BSA complex have also been studied. Whereas the absorption spectrum of curcumin is redshifted, the fluorescence spectrum of curcumin was blueshifted in the presence of BSA. The fluorescence quantum yield of curcumin on complexing with BSA was approximately 0.05. Steady-state fluorescence anisotropy studies showed a significant increase in the anisotropy value of 0.37 in BSA-bound curcumin. The fluorescence decay of the curcumin-BSA complex followed a biexponential decay with fluorescence lifetimes of 413 ps (33%) and 120 ps (67%). On the basis of these complementary results, it has been concluded that curcumin shows very high binding to BSA, probably at the hydrophobic cavities inside the protein.

The complex between 9-(n-decanyl)acridone and Bovine Serum Albumin. Part 2. What do fluorescence probes probe?

Factor analysis indicates that the fluorescence spectrum of 9-(n-decanyl)acridone (NDA), when bound to Bovine Serum Albumin (BSA), can be described quite adequately as the sum of two spectra, attributed to a "free" and a "bound" species. Kinetic evidence indicates that upon electronic excitation the system undergoes a net increase in free NDA, relative to the equilibrium distribution in the ground state, which would be consistent with Lewis acid sites on BSA being responsible for the binding. The system does not attain a position of equilibrium during the duration of the excited singlet state. This permits the determination of excited state rate constants for binding and unbinding of NDA on BSA, as well as the decay constants for the two forms of the probe.