V. Prakash

Extractability of polyphenols of sunflower seed in various solvents

The extractability of chlorogenic acid from defatted sunflower seed flour in water and salt solutions at different pH values and also in aqueous organic solvents was determined. It increased with increase in pH and at pH 8 in water nearly 70% chlorogenic acid was removed in a single extraction, while NaCl did not increase the extraction, and, MgCl2 and CaCl2 increased it, especially at higher concentrations. Methanol, ethanol, isopropanol and acetone, at 20% concentration in water, caused the maximum extraction of polyphenol. These organic solvents without added water were poor solvents for the extraction of polyphenol from the flour.

Partial specific volumes and interactions with solvent components of α-globulin fromSesamum indicum L. in urea and guanidine hydrochloride

The interaction of α-globulin with urea/guanidine hydrochloride was investigated by determining the apparent partial specific volumes of the protein in these solvents. The apparent partial specific volumes were determined both under isomolal and isopotential conditions. The preferential interaction parameter with solvent components calculated were 0.08 and 0.1 g of urea and guanidine hydrochloride respectively per g protein. In both the cases the interaction was not preferential with water. The total binding of denaturant to α-globulin was calculated both for urea and guanidine hydrochloride and the correlation between experimentally determined number of mol of denaturant bound per mol of protein and the total number of peptide bonds and aromatic amino acids were found to be in excellent agreement with each other. The changes in volume upon transferring α-globulin from a salt solution to 8 M urea and 6 M guanidine hydrochloride were also calculated.

Structural similarities among the high molecular weight protein fractions of oilseeds

Data on the physico-chemical properties of proteins from soybean, groundnut, sesame seed, sunflower seed, safflower seed, mustard seed, rapeseed and cotton seed are fairly extensive. An examination of the available data on high molecular weight proteins suggests that there are similarities in many of their properties. In this report the similarity in amino acid composition, size and shape, molecular weight, secondary structure, subunit composition, association-dissociation at high and low pH, stability towards denaturants, hydrolysis by enzymes and quaternary structure of the high molecular weight proteins is discussed. Based on these similarities a model has been proposed for the associationdissociation, denaturation and reassociation behaviour of the high molecular weight proteins of oilseeds.

Association-dissociation of glycinin in urea, guanidine hydrochloride and sodium dodecyl sulphate solutions

The effect of urea, guanidine hydrochloride and sodium dodecyl sulphate on glycinin, the high molecular weight protein fraction from soybean has been investigated by analytical ultracentrifugation. Urea and guanidine hydrochloride dissociate the protein to a ‘2S’ protein through the intermediary 7S and 4S proteins. Howeαer, in sodium dodecyl sulphate the protein directly dissociates to a 2S protein. Analysis of the data by calculation of per cent fraction and S20,w value indicates that dissociation and denaturation of glycinin occur simultaneously in the presence of the aboαe reagents but to different extents.

Studies on the conformation of α-globulin fromSesamum indicum L. in cationic and nonionic detergents

The circular dichroic spectra of α-globulin fromSesamum indicum L. was recorded in the presence of cetyltrimethyl ammonium bromide, Triton X-100 and Brij-36T. The protein in 0.2 M phosphate buffer pH 7.4 had about 25% Β-structure and 5% α-helix, the rest being aperiodic or irregular structure and a-helix, structure was increased by cationic detergent cetyl trimethyl ammonium bromide. But, the increase in α-helix content was much less than that induced by an anionic detergent, sodium dodecyl sulphate. In non-ionic detergent like Brij-36T and Triton X-100, specific Β-structures like II-Β and I-Β were formed along with changes in α-helical and aperiodic structures. These results suggest that the protein has a fairly labile quaternary structure.

Hydrodynamic properties of α-globulin fromSesamum indicum L.

The protein α-globulin fromSesamum indicum L. has been characterised for its size and shape using αarious chemical, physico-chemical and hydrodynamic properties. The protein has an S20,w0 of 12.8, D20,w °f 4.9 × 10-7 cm2/sec and a partial specific αolume of 0.725 ml/g in the natiαe state. The intrinsic αiscosity of the protein was determined to be 3 0 ml/g indicating it to be globular in shape. The molecular weight of the protein as determined by αarious approaches in analytical ultracentrifugation αaries from 2.6–2.74 × 105. The molecular weight from sedimentation equilibrium yields a αalue of 2.74 × 105 in the natiαe state and a αalue of 19000 in the dissociated and denatured state in 6 M guanidine hydrochloride. The eαaluation of frictional ratios using Stokes radius and results from electron microscopy confirms the protein to be globular in shape. The protein consists of at least 12–14 subunits. The eαaluation of hydrophobic parameters and energetics of interaction of subunits indicate that the protein is stabilized predominantly by hydrophobic interactions.

Interaction of 3’-O-caffeoyl D-quinic acid with multisubunit protein helianthinin

Chlorogenic acid, 3’-O-caffeoyl D-quinic acid, is an inherent ligand present inHelianthus annuus L. The effect of pH on chlorogenic acid binding to helianthinin suggests that maximum binding occurs at pH 6.0. The protein-polyphenol complex precipitates as a function of time. The association constant of the binding of chlorogenic acid to helianthinin, determined by equilibrium dialysis, at 31°C has a value of 3.5 ± 0.1 × 104M−-1 resulting in a ΔG value of − 6.32 ± 0.12 kcal /mol. The association constantKais 1.0 ± 0.1 × 104M−1 as determined by ultraviolet difference spectral titration at 25°C with ΔG° of -5.46 ± 0.06 kcal/mol. From fluorescence spectral titration at 28°C, theKavalue is 1.38 ± 0.1 × 1 0 4M−1 resulting in a ΔG of − 5.70 ± 0.05 kcal/mol. The total number of binding sites on the protein are 420 ± 50 as calculated from equilibrium dialysis. Microcalorimetric data of the ligand-protein interaction at 23°C suggests mainly two classes of binding. The thermal denaturation temperature,Tmof the protein decreases from 76°C to 72°C at 1 × 10−3M chlorogenic acid concentration upon complexation. This suggests that the complexation destabilizes the protein. The effect of temperature onKaof chlorogenic acid shows a nonlinear increase from 10.2°C to 45°C. Chemical modification of both lysyl and tryptophanyl residues of the protein decreases the strength of binding of chlorogenic acid. Lysine, tryptophan and tyrosine of protein are shown to be present at the binding site. Based on the above data, it is suggested that charge-transfer complexation and entropically driven hydrophobic interaction are the predominant forces that are responsible for binding of chlorogenic acid to the multisubunit protein, helianthinin.

Molecular interactions between ribosomal proteins — An analysis of S7-S9, S7-S19, S9-S19 and S7-S9-S19 interactions

Ribosomal proteins S7, S9 and S 19 fromEscherichia coli have been studied by the sedimentation equilibrium technique for possible intermolecular interaction between pairs of proteins as well as in a mixture of 3 proteins. The proteins were isolated to a purity greater than 95% and were characterized in the reconstitution buffer. It was observed that none of the proteins has a tendency to self-associate in the concentration range studied in the temperature range 3–6°C. Protein S9 behaves differently in the presence of other proteins. Analysis of the sedimentation equilibrium data for S7-S9, S9-S19 and S7-S9-S19 complexes revealed the need for considering the presence of a component of higher molecular weight in the system along with the monomers and their complexes to provide a meaningful curve-fitting of the data. Proteins S7 and S19 were found to interact with an equilibrium constant of association of 3 ± 2 × 104 M−1 at 3°C with a Gibbs free energy of interaction ΔG° of −5·7 kcal/mol. These data are useful for the consideration of the stabilization of the 3 0S subunit through protein-protein interactions and also help in building a topographical model of the proteins of the small subunit from an energetics point of view.