Bovine serum albumin solution osmotic pressure

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 ... 

The osmotic pressure of salt-free (electrodialyzed) bovine serum albumin solutions was measured at pH = 5.37 ( ). At this pH the net charge of the protein molecules is zero. The following data were obtained in different runs ... 

To examine the potential of this new approach, we analyze the experimental data for the osmotic pressure of bovine serum albumin (BSA) in 0.15 mol dm-3 sodium chloride [112] and human serum albumin (HSA) solution in 0.1 molx dm-3 phosphate buffer [111]. According to a previous experimental and theoretical study [111] the two solutions differ substantially in the degree of protein association. The theoretically determined osmotic coefficient can be fitted to the experimental results to obtain the fraction of dimers in the solution. The results of our analysis are presented in Figs. 11 and 12. The protein molecular weights used in these calculations were 69,000 g/mol for BSA and 66,700 g/mol for HSA. The hard-sphere diameter of spherical proteins was assumed to be 6.0 nm. For the case of the multicomponent model, the ions of the low-molecular weight +1 — 1 electrolyte were modelled as charged hard spheres with diameter 0.4 nm. 

Vilker, V.L., Colton, C.K., and Smith, K.A. The osmotic-pressure of concentrated protein solutions - effect of concentration and ph in sahne solutions of bovine serum-albumin. Journal of Colloid and Interface Science, 1981, 79, No. 2, p. 548-566. 

To test the quantitative predictions of the model, we measured the disaggregation of the hemoglobin tetramer by the increase in osmotic pressure with pH (5). When the pressure is compared to that observed in solutions of bovine serum albumin (BSA a protein of comparable molecular weight that does not disaggregate), we can ascribe the difference in pressure to disaggregation. In the titration of both protein solutions, the minimum pressure occurs at the isoelectric point (IEP), which is 6.82 0.06 for hemoglobin at 25.0 °C. 

An aqueous solution of the protein bovine serum albumin, containing 2.00 x 10 g of protein per cubic centimeter, has an osmotic pressure of 8.1 x 10 bar at 0°C. Estimate the molar mass of this protein. 

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