Partial specific volume measurement

The significance of such a difference between the partial specific volumes measured at constant chemical potential (v2,n3) and constant... 

For the denaturation of / -Lg in 40% 2-chloroethanol, the presently reported partial specific volume measurements result in a AV value of —590 ml/mole. This value is very close to that previously reported for the denaturation of this protein by 6.4M urea, —610 ml/mole (27). Although this similarity of AV values is striking, it might be the result of a fortuitous compensation of various effects. The change in volume calculated from the difference in partial specific volumes is the sum of a number of contributions (28), such as differences in electrostriction in the two media, changes in the density of solvent components when they interact... 

The diffusion constant, measured with three different apparatuses in differently constructed cells, was found to be equal to = 4.90 0.05. Mallette and Dawson (1949) reported for their preparation a value of D qW = 6.1 this higher value is easily explained by the presence of lighter impurities (between 10-20%). The partial specific volume, measured in pycnometers, was found to be 0.758 ml./gm. 

The view that the clay surface perturbs water molecules at distances well in excess of 10 A has been largely based on measurements of thermodynamic properties of the adsorbed water as a function of the water content of the clay-water mixture. There is an extensive literature on this subject which has been summarized by Low (6.). The properties examined are, among others, the apparent specific heat capacity, the partial specific volume, and the apparent specific expansibility (6.). These measurements were made on samples prepared by mixing predetermined amounts of water and smectite to achieve the desired number of adsorbed water layers. The number of water layers adsorbed on the clay is derived from the amount of water added to the clay and the surface area of the clay. 

Sedimentation equilibrium Absolute requires only centrifuge measurements and partial specific volume of solute Time-consuming measurement and interpretation somewhat limited mol. wt. range 5... 

What is obtained by performing such experiments across an appropriate temperature range is the precise measurement of the coefficient of thermal expansion for protein partial specific volumes that may be detected at concentrations... 

EXAMPLE 3.3 Excluded Volume of Bovine Serum Albumin from Osmotic Pressure Measurements. A plot of 7r/c versus c for an aqueous solution of the bovine serum albumin molecule at 25°C and pH = 5.37 is shown in Figure 3.6. The molecule is known to be nearly spherical and uncharged at this pH. Evaluate the molecular weight and the excluded volume of this protein from the intercept and slope of this line, 0.268 torr (g kg-1)-1 and 1.37 10 3 torr kg2 g 2, respectively. From the particle mass and volume, estimate the partial specific volume of the solute in solution. The specific volume of the unsolvated protein is about 0.75 cm3 g 1 does the solute appear to be solvated ... 

Here c(r) is the concentration c at the radial position r (measured from the centrifuge axis), a is the radial distance of the meniscus, M is the molecular mass in daltons, and v is the partial specific volume in ml/gram. For most proteins v varies from 0.69-0.75. It is the reciprocal of the density of the particle. Rho (p) is the density (g/ml) of the solvent. A plot of log c(r) against r2 is a straight line of slope M (1 -up) / 2RT. The computer can also accommodate mixtures of proteins of... 

Here M is molecular weight, R is the gas constant, T is the absolute temperature in degrees Kelvin, V is the partial specific volume of the solute, p is the density of solution, w is the angular velocity, r is the distance from the center of rotation, and c is the concentration measured at r. Under... 

Lactoglobulin A in 40% 2-Chloroethanol. Previous light scattering and differential refractometry measurements (8, 23) have shown that / -lactoglobulin exhibits strong preferential interactions with solvent components in the water-2-chloroethanol system. Since the preferential interaction between protein and 2-chloroethanol in this system was found to be maximal at 40% (v/v), the effect of this interaction on the partial specific volume of the protein was determined. 

The densities of the solvent and of / -lactoglobulin A ( -Lg) in 40% (v/v) 2-chloroethanol, in the presence of 0.01 M HC1 and 0.02M NaCl, were determined, with and without prior dialysis, in a 10-ml pycnometer at 20°C. Solutions were prepared as described previously (8, 24). The solutions were filtered through millipore filters in syringe adapters just before the density measurements. Protein concentrations were determined after filtration by ultraviolet absorption at 278 nm. The apparent partial specific volume, oapp, was calculated from the densities using the standard equation (21, 25) ... 

In all measurements, the heating rate was 1 °C min-1. The partial molar heat capacity of a fully extended peptide is calculated from its amino acid composition according to the method of Privalov and Makhatadze.1 37 Partial specific volume of the peptides was calculated from amino acid composition according to Makhatadze et al.,[138l with a value of 0.751 mL-mg-1. 

Partial specific volumes were calculated from density measurements on poloxamer solutions made using a digital density meter (Paar DMA 02C). 

A value of 2.5 was assigned to the viscosity increment, v, assuming micellar sphericity. The partial specific volume, v, was determined from density measurements. 

Pure adrenodoxin can be obtained by either procedure A or B when the steps of DEAE-cellulose chromatography and Sephadex G-75 passage are repeated. Fig. 1 shows data of the sedimentation equilibrium experiment the result indicates that the molecular weight is approximately 12,000. From sedimentation velocity experiments, the sedimentation constant (Szo.w) was calculated to be 1.55 S. The diffusion constant (Z)2o, w) measured in a Neurath cell was computed to be 11 x 10-7 cm2/sec. The determination of partial specific volume by measurement of the... 

Cohen G, Eisenberg H (1968) Deoxyribonucleate solutions Sedimentation in a density gradient, partial specific volumes, density and refractive index measurements, and preferential interactions. Biopolymers 6 1077-1100... 

To evaluate molar masses from equilibrium runs it is necessary to know (very accurately) the value of the partial specific volume of the species. The partial spedfic volumes of proteins and nucleic acids are not dependent on conformation so they can be evaluated from the amino acid or nucleotide composition (Laue et al. 1992). A satisfactory working value for proteins is v = 0.735 10-3 m3 kg-1. Partial specific volumes can also be measured by comparison of equilibrium runs carried out in H20, D20 and H280, using the different densities of the three isotopic forms of water. 

Here M is the molecular weight and V the partial specific volume of the solute, N the Avogadro number, k the Boltzmann constant, and T the absolute temperature s and D are the sedimentation and translational diffusion coefficients (after extrapolation to infinite dilution). The translational frictional coefficients from both measurements are regarded as identical, i.e., f, = fd. The rotary frictional coefficient, designated as f, can be determined from either flow birefringence or non-Newtonian viscosity measurements. 

The particle weight (from sedimentation, diffusion and partial specific volume data) was calculated as 12.1 X 10 . The frictional ratio,/// , 1.59, corresponded to an axial ratio of 11, the particle being depicted as an elongated ellipsoid. Similar measurements with liver glycogen gave a particle weight of 13.2 X 10 (based on viscosity increment and diffusion data). 

For molecular modeling of the lipoproteins, values for the partial specific volumes of the lipoprotein components are required. The partial specific volume of an aqueous egg yolk lecithin suspension is 0.984 ml/g (Hauser and Irons, 1972), and this provides a reasonable approximation for the partial specific volume of the phospholipid occupying the surface monolayer of a lipoprotein. The reciprocal of the density of liquid triolein (Small, 1986) yields its partial specific volume, 1.102 ml/g, and provides a reasonable approximation for triglyceride dissolved in the cholesteryl ester-filled core of the LDL. For cholesterol, the partial specific volume of 1.021 ml/g measured in benzene (Haberland and Reynolds, 1973) has been employed. The value of 0.740 ml/g employed for the partial specific volume of apoBlOO was determined from its amino acid composition (Lee et al., 1987). A value of 0.60 ml/g was used for the partial specific volume of the carbohydrate moiety. One important parameter, the partial specific volume of cholesteryl ester, remains to be determined. As will be shown below, its value is estimated to be 1.058 ml/g. 

The primary technical limitation on the accuracy of molecular weights so determined is the sedimentation constant. Since the molecular weight is directly proportional to the sedimentation constant, where S is low, small errors in S will be relatively important. For -dextrin with S = 0.47, if S is in error by only 0.02 (an average error for measurements of this sort) this will give an error of 50 in the molecular weight. A second essential factor which so far has not been determined with high precision is the partial specific volume of the carbohydrate. Nevertheless, it has been possible to obtain molecular weights which are within a few perct nt of the theoretical values (see Table IV). 

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