1. Protein adsorption at solid-liquid interfaces: Part IV--Effects of different solid-liquid systems and various neutral salts
S Hajra, D K Chattoraj Indian J Biochem Biophys. 1991 Aug;28(4):267-79.
Adsorption isotherms of BSA at the solid-water interfaces have been studied as a function of protein concentration, ionic strength of the medium, pH and temperature using silica, barium sulphate, carbon, alumina, chromium, ion-exchange resins and sephadex as solid interfaces. In most cases, isotherms for adsorption of BSA attained the state of adsorption saturation. In the presence of barium sulphate, carbon and alumina, two types in the isotherms are observed. Adsorption of BSA is affected by change in pH, ionic strength and temperature of the medium. In the presence of metallic chromium, adsorbed BSA molecules are either denatured or negatively adsorbed at the metallic interface. Due to the presence of pores in ion-exchange resins, adsorption of BSA is followed by preferential hydration on resin surfaces in some cases. Sometimes two steps of isotherms are also observed during adsorption of BSA on the solid resins in chloride form. Adsorption of BSA, beta-lactoglobulin, gelatin, myosin and lysozyme is negative on Sephadex surface due to the excess adsorption of water by Sephadex. The negative adsorption is significantly affected in the presence of CaCl2, KSCN, LiCl, Na2SO4, NaI, KCl and urea. The values of absolute amounts of water and protein, simultaneously adsorbed on the surface of different solids, have been evaluated in some cases on critical thermodynamic analysis. The standard free energies (delta G0) of excess positive and negative adsorption of the protein per square meter at the state of monolayer saturation have been calculated using proposed universal scale of thermodynamics. The free energy of adsorption with reference to this state is shown to be strictly comparable to each other. The magnitude of standard free energy of transfer (delta G0B) of one mole of protein or a protein mixture at any type of physiochemical condition and at any type of surface is observed to be 38.5 kJ/mole.
2. Measurements of proton relaxation time T2 on cattle eyes lenses
A Gutsze, D Deninger, R Olechnowicz, J A Bodurka Lens Eye Toxic Res. 1991;8(2-3):155-62.
A simple two phase model does not explain the temperature dependence of T1 relaxation time in lenses as biological systems. Therefore, a distribution of correlation times of water particles has to be assumed by a certain distribution of the water protein binding energy. As a consequence, from the temperature dependence of T1 relaxation time, the activation energy of water molecules in the lens cannot be evaluated directly without the knowledge of the distribution width. This problem can be solved by T2 measurements in lenses. From the slope of T2 as a function of temperature, mean activation energy can be calculated independently on the distribution width. Measurements were performed on lenses originating from 5-7 years old cows, 2-year old bull-calfs and a 12-year old bull in the temperature range -30 to +105 degrees C. It could be demonstrated that about 80% of water behaves as liquid-like water with an activation energy 14 +/- 4 kJ/mol corresponding to the value of free water. The remaining water (about 20%) is bound to the protein with an activation energy of 20 +/- 5 kJ/mol. At 42 degrees C the protein denaturation process starts in the eye lens and will be completed by 70 degrees C, yielding a protein bound-water complex.
3. Determination of the effective correlation time modulating 1H NMR relaxation processes of bound water in protein solutions
Ali Yilmaz, Hatice Budak, F Sadan Ulak Magn Reson Imaging. 2008 Feb;26(2):254-60. doi: 10.1016/j.mri.2007.05.008. Epub 2007 Aug 1.
The relaxation in protein solutions has mainly been studied by nuclear magnetic relaxation dispersion (NMRD) techniques. NMRD data have mostly been analyzed in terms of fast chemical exchange of water between free water and water bound to proteins. Several approaches were used for the estimation of correlation time modulating the relaxation mechanism of bound water. On the other hand, in a nuclear magnetic resonance experiment, the relaxation rates of protein solutions (1/T1 and 1/T2) and also those of free water (1/T1f and 1/T2f) are measurable. However, the relaxation rates of bound water (1/T1b and 1/T2b) are not. Despite this, equating (1/T1-1/T1f)/2(1/T2-1/T2f) to (1/T1b)/2(1/T2b) leads to an expression involving only an effective tau that is related to the rotational correlation time (tau r) of proteins. Equating the ratios may therefore give a simple alternative method for the determination of tau r even if this method is limited to a single resonance frequency. In this work, a formula was derived for the solution of the effective tau. Then, the 1/T1 and 1/T2 in solutions of two globular proteins (lysozyme and albumin) and one nonglobular protein (gamma-globulin) were measured for different amounts of each protein. Next, the values of 1/T1 and 1/T2 were plotted vs. protein concentrations, and then the slopes of the fits were used in the derived equation for determining the effective tau values. Finally, the rotational correlation time tau r, calculated from tau, was used in the Stokes-Einstein relation to reproduce relevant radii. The effective tau values of lysozyme, albumin and gamma-globulin were found to be 5.89 ns, 7.03 ns and 8.8 ns, respectively. tau r values of albumin and lysozyme produce their Stokes radii. The present data suggest that use of the measurable ratio in the derived formula may give a simple way for the determination of the correlation times of lysozyme and albumin.
