• Meenakshi Maruthamuthu

      Articles written in Journal of Chemical Sciences

    • Binding of ketoprofen with bovine serum albumin

      Meenakshi Maruthamuthu Sankaran Kishore

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      The binding of Ketoprofen, i.e 2-(3-benzoylphenyl) propionic acid, with bovine serum albumin, BSA, was investigated by equilibrium dialysis. Limiting the studies to low drug (10 to 100 μM) concentrations, the binding data correspond to a single set of binding sites, namely, the high-affinity sites. Scatchard and Klotz methods of analysis have been employed to determine the binding parameters for the high-affinity sites. The binding constant does not vary significantly with [BSA] in the concentration range 7·25 to 21·5 μM. The molar ratio, [drug]/[protein] is found to be a critical factor in determining the nature and number of binding sites. The quenching of intrinsic fluorescence of the protein at the emission wavelength of 346 nm indicates the presence of tryptophan in the binding site.

    • Binding of naproxen to bovine serum albumin and tryptophan-modified bovine serum albumin

      Meenakshi Maruthamuthu S Kishore

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      Two classes of binding sites, a single high-affinity site with an association constant of 4·8×106 M−1 and two low-affinity sites with association constant of about 0·05×106 M−1 have been observed in the interaction of Naproxen with bovine serum albumin (BSA). Chemical modification of two tryptophan residues in BSA with 2-hydroxy-5-nitrobenzyl bromide has led to a reduction in the association constant of the high-affinity site by 89% and its number of binding sites by 66% suggesting the involvement of tryptophan residues in the high-affinity site. In contrast, the two low-affinity sites were not affected by the modification. Binding of Naproxen to the low-affinity sites of BSA induces microdisorganisation of the albumin structure leading to conformational changes as evident from fluorescence measurements with 1-anilino-8-naphthalenesulphonic acid as the probe.

    • Binding of 1-anilinonaphthalene-8-sulphonate to poly (N-vinyl-2-pyrrolidone)

      Meenakshi Maruthamuthu E Subramanian

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      The binding of 1-anilinonaphthalene-8-sulphonate (ANS) to poly(N-vinyl-2-pyrrolidone) (PVP) of molecular weight grades k30 (molecular weight 40,000) and k90 (360,000) was studied by a dialysis technique in 0·05 M phosphate buffer, pH 7·1, at different temperatures. The intrinsic binding constant,K, was determined. The binding was favoured by negative enthalpy and positive entropy in both the systems indicating respectively that energetic forces and hydrophobic interactions were contributing to the binding affinity. The effects of addition of urea and palmitic acid on binding were investigated by dialysis and fluorescence techniques. The results showed that the binding of ANS to PVP was dependent on the nature and microenvironment of the binding sites and thereby pointed out the importance of the iceberg structure of water in the binding system.

    • Bromocresol green as a new spectrophotometric probe for serum albumins

      Meenakshi Maruthamuthu S Kishore

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      Bromocresol green (BCG) has been employed as a new spectrophotometric probe to characterise the binding regions of human serum albumin (HSA) and bovine serum albumin (BSA). BCG binds with greater affinity onto BSA than onto HSA. Based on the abilities of ligands Naproxen and l-anilino-8-naphthalenesulphonic acid (ANS) to displace BCG from the serum albumins by competitive or non-competitive mechanism, binding regions were identified for these ligands. It has been found that both Naproxen and ANS share common binding sites with BCG in HSA with the relative ability of Naproxen > ANS on binding to HSA. In the case of BSA, ANS competes with BCG for the same binding sites, whereas Naproxen exhibits non-competitive binding. The highaffinity sites of Naproxen coincide with BCG binding sites while the low-affinity sites occur at sites distinct from the BCG binding region.

    • Interaction of 1-anilinonaphthalene-8-sulphonate with cross-linked poly (N-vinyl-2-pyrrolidone)

      Meenakshi Maruthamuthu E Subramanian

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      The interaction of 1-anilinonaphthalene-8-sulphonate (ANS) with cross-linked poly(N-vinyl-2-pyrrolidone) (CPVP) was studied by the adsorption technique at different temperatures and at two different pH values. Analysis by the Scatchard method and the study made in the presence of urea showed that the iceberg structure of water affects the sorption of ANS to CPVP, leading to cooperativity. The observed Giles sorption isotherms at both the pH values were of theL-type which indicated the interaction of ANS in flat configuration with the binding site in CPVP. The sorption of ANS to CPVP was enhanced considerably at acidic pH due to some structural factors which also resulted in multilayer sorption at this pH. Comparison of binding of ANS to CPVP and to linear poly(N-vinyl-2-pyrrolidone) demonstrated the greater contribution of hydrophobic interaction in CPVP than in the linear polymer.

    • Heterotropic binding of alclofenac and dansylsarcosine to bovine serum albumin

      Meenakshi Maruthamuthu S Kishore

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      The binding data for the interaction of alclofenac (AF) and dansylsarcosine (DS) to bovine serum albumin (BSA) have respectively yielded nonlinear Scatchard plots. The plots have been subjected to Rosenthal’s method of analysis and thus the ligands have been found to possess two different kinds of sites in BSA. The binding capacities of these sites have been evaluated. The fluorescence competition studies have revealed that the binding of DS to BSA is noncompetitively inhibited by AF. Therefore, the presence of distinct binding sites for AF and DS in BSA could be inferred. The fluorescence quenching studies have also been able to demonstrate this aforesaid fact. The analysis of the quenching data by the modified Stern-Volmer plot has indicated that both the tryptophan (Trp) residues of BSA are accessible to DS for the quenching in absence of AF, but only one of them is accessible in presence of AF. This has led to suggest that the binding site of DS has been in the vicinity of loop 3–4, involving Trp-134 and Trp-212. The binding of AF at a distinct site from that of DS has exerted heterotropic interactions at the DS binding site and thereby inhibited the binding of DS to BSA.

    • Polymer-ligand interaction studies. Part I. Binding of some drugs to poly(N-vinyl-2-pyrrolidone)

      Meenakshi Maruthamuthu E Subramanian

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      A physico-chemical investigation on the binding of some nonsteroidal anti-inflammatory drugs, Naproxen (NP) and Ketoprofen (KP) and a drug model compound, salicylic acid (SA) to poly(N-vinyl-2-pyrrolidone) (PVP, molecular weight = 360,000), was performed at pH 7.1 by the fluorescence competition method employing 1-anilinonaphthalene-8-sulphonate (ANS) as the fluorescent probe. The binding affinities of these substrates to PVP are in the order KP < SA < NP which has been explained on the basis of their structural features and the consequent effect on the interacting forces. Theπ-π interaction between the carbonyl group of PVP and theπ-ring system of the substrate molecule seems to be crucial in deciding the binding affinities of the substrates

    • Binding of rose bengal onto bovine serum albumin

      S Kishore Meenakshi Maruthamuthu

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      The binding of rose bengal (RB) to bovine serum albumin (BSA) occurs with both the folded (atpH 7·4) and the unfolded (pH 12·7) forms of BSA. Absorption spectroscopy has revealed an identical red-shift of 15nm in λmax of RB in presence of BSA both atpH 7·4 and 12·7. The affinity constants (K) atpH 12·7 have been reduced only by 50% in magnitude from those atpH 7·4. These lead us to infer that neither disulphide loops nor buried residues are involved but that the binding of RB occurs at the sites near the surface of BSA. Moreover, the drastic alterations in the near-UV circular dichroism suggest tertiary structural changes induced by RB on binding to BSA. The conformational changes at the binding sites of BSA atpH 7·4 and the affinity of RB particularly towards the exposed residues in BSA atpH 12·7 are the significant factors in the binding of RB to BSA.

    • Selective quenching of tryptophanyl fluorescence in bovine serum albumin by the iodide ion

      Meenakshi Maruthamuthu G Selvakumar

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      Modified Stern-Volmer equation is obeyed by bovine serum albumin (BSA)-iodide system showing selective quenching of tryptophanyl fluorescence of BSA. The fraction of accessible protein fluorescence is 0.56 and the effective Stern-Volmer constant is 290 M-1 at pH 7.4 in 0.005 M phosphate buffer at 25°C. Collisional quenching is operative both in the BSA -I−1 system and the model system, tryptophan-I−1. It is supported by the observed relationship between the ratio of quenching rate constants (kq) and diffusion coefficients and alsokq with bulk viscosity.

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