Partial specific volume calculation

The P subunit sedimented as a single sharp band with S20fW= 3.54 +/- 1.9% (not shown). Using the diffusion coefficient and partial specific volume calculated for R.rubrum, a molecular weight of 45,000 was calculated which suggests that the P subunit (molecular weight 54,000) exists as a monomer in solution. This is supported by the fact that P coeluted with BSA (molecular weight 66,700) after gel filtration. 

Based on the assumption that the total specific volume can be calculated as the sum of the partial specific volumes of the initial and forming components, and expressed pj by TaF5 molar fraction - N,- using equation (64), an equation representing the total variable density of the melt (p ) can be written as follows ... 

The partial specific volume is the increase in the volume of a solution caused by the presence of the solute and is defined as the volume occupied by 1 kg of the solute in 100 kg of the solution. The value may be calculated using the densities of both the solvent (p) and the solution (ps) ... 

The radius of the peptide molecule can be calculated from the molecular mass, Avogadro number, and the partial specific volume. 

Equation (32) has been compared with phase boundary concentration data in the following way. For each solution, N of the polymer sample is estimated from Mw or the viscosity-average molecular weight Mv along with the molecular parameters ML and q listed in Table 1, and d is calculated with d from II or 0II/0c data. For systems which lack these data, the values of d from the (partial) specific volume vsp may be substituted. Table 2 lists the resulting values of d from II, 0II/0c, or vsp for various systems. The phase boundary volume fractions vc v ( = vc v v = I and A) are calculated from experimental phase boundary weight fractions (or mass concentrations) with d, Mw (or Mv), and Ml. Finally, with these numerical results, [vc v/dav(d)] — AV(N, d) is computed... 

Sedimentation. The sedimentation experiments are tabulated in Tables I and II. In Table I typical sedimentation coefficients determined in H20 and D20 are in close agreement here and with previously reported values determined for both protio and deuterio phycocyanin from F. calothricoides (15,16). Each of the tabulated coefficients is for a single experiment at an approximate protein concentration of 15 mg. per ml. Lyophilizing a phycocyanin preparation twice had little effect on the observed sedimentation coefficients. In calculating the S values the same partial specific volume of the protein was used for both D20 and H20. This practice is consistent with the recent results of Edelstein and Schach-man (7). Small increases in sedimentation coefficients from H20 to D20 are to be expected because of deuterium substitution on exchangeable positions. The slope of an S vs. concentration plot for phycocyanin in H20 and D20 would also probably differ. Consequently, small changes in S from H20 to D20 would be expected at a constant protein concentration. 

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) ... 

Knowledge of the partial specific volume of a protein in the denaturant, t>2,03, which is essential for determining its molecular weight by small-angle x-ray scattering, permits also the calculation of the volume change upon denaturation since... 

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... 

With use of the. s 2°0w and D°o,w values cited below (Section II,D,1) an additional estimate of the molecular weight can be made by means of the Svedberg equation (18) the value obtained is 118,000. [Calculations employ as partial specific volume v = 0.745 cm3/g, obtained from the amino acid composition of the protein given in Table III (IP).]... 

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. 

With additional information, including the heat capacity of the buffer solvent, the partial specific volumes (volume per gram of the solute), and the specific volume of the solvent, one can extract the partial specific heat capacity (J K 1g I) of the solute. Privalov has summarized these calculations.8 Because the solutions are studied at very low concentrations, it is assumed that the contribution to the total heat capacity from the solvent cancels out when one calculates the excess heat capacity. With only minor exceptions, the procedures used to calculate parameters associated with the transformations in nucleic acids and in proteins are the same and yield quantities that are interpreted in similar ways, although researchers in these two fields may use a different notation for the same quantity. 

For the analysis of light scattering experiments the refractive indices of the DADMAC/AAM solutions at dialysis equilibrium were determined, showing the validity of the additivity principle [67]. The additivity could also be proven for the partial specific volumes which are necessary to calculate molar masses from ultracentrifugation experiments [131]. These dependencies are summarized in Fig. 24. 

The partial specific volume of the protein was 0.75 cm3 g 1 and the density of the solution (assumed constant) was 1.00 g cm"3. Calculate the relative molecular mass of the protein. 

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

The behavior of the optical system is assessed by plotting In c (absorbance in this case) vs. r. The plot should be linear and the molecular weight calculated from the known partial specific volume and the other constants should agree closely with the known value, typically within 1 or 2%. 

The values for the molecular weight of plant ferredoxins reported by different investigators are not in agreement. Appella and San Pietro 4) reported a molecular weight of 17,000 for spinach ferredoxin, based on an S2o,w of 1.36 and a diffusion coefficient of 6.6 X 10 7 cm2/sec. The partial specific volume was assumed to be 0.71. A calculation by the writer for the minimal molecular weight of spinach ferredoxin from available amino acid composition data Fry and San Pietro (47)) and the assumption of six cysteine residues per mole gave a value of 13,000. Arnon (5)... 

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... 

The purified testis protein as prepared maintained a single homogeneous boundary in ultracentrifugation. The sedimentation constant (S20, w) was calculated to be 1.9 S on the assumption of a partial specific volume of 0.72. 

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