Diffusion Coefficients of Proteins

Capillary zone electrophoresis, an up-to-date high resolution separation method useful for proteins and peptides, has been shown to be a useful method for determining electrophoretic mobilities and diffusion coefficients of proteins [3], Diffusion coefficients can be measured from peak widths of analyte bands. The validity of the method was demonstrated by measuring the diffusion coefficients for dansylated amino acids and myoglobin. 

The low molecular diffusion coefficients of proteins and other biopolymers reduces the efficiency of mass transfer and compromises efficiency as flow rate is increased. Therefore, high-performance SEC columns are usually operated at modest flow rates, e.g., 1 ml/min or less. However, operation at very low flow rates is undesirable due to excessive analysis times, loss of efficiency due to axial analyte diffusion, and the risk of poor recovery due to analyte adsorption. 

Measurement and Interpretation of Diffusion Coefficients of Proteins Louis J. Costing... 

Gosting, L. J. Measurement and interpretation of diffusion coefficients of proteins in Advances in Protein Chemistry, Vol. 11, p. 429 (ed. M. L. Anson, K. Bailey and J. T. Edsall), New York Academic Press 1956. 

N. Baden and M. Terazima. A novel method for measurement of diffusion coefficients of proteins and DNA in solution. Chem. Phys. Lett., 393, 539-45 (2004)... 

Fig. 12. Translational diffusion coefficients of protein 4 determined at different scattering angles (6) are plotted against their corresponding K2 values where K = (4irn/ ) sin (0/2). This anomalous behavior is due to sample heterogeneity. From Ahmed et al. (1975), reproduced with permission.

Trumit (1954) has described two closely related methods for determining diffusion coefficients of proteins based on measurement of the rate of adsorption of protein from a dilute solution on to a Blodgett— Langmuir slide. One method employs stirred conditions so that the... 

M. Ibrahim, Z. Gongwei, Z. Junjie, Determination of diffusion coefficients of proteins by flow injection analysis and its application to estimation of molecular masses of proteins, Instrum. Sci. Technol. 26 (1998) 333. 

Keller, K., E. Canales, and S. Yum, Tracer and mutual diffusion coefficients of proteins. Journal of Physical Chemistry, 1971, 75, 379-387. 

The protein sample can be introduced at any place in the gradient. It is usually introduced into the gel together with the ampholyte solution. The protein is then focussed at the same time as the pH gradient develops. Due to the low diffusion coefficients of proteins, they form much sharper bands than the ampholytes themselves. The ampholyte molecules have relatively low molecular weights (< 1 kDa) and thus high diffusion coefficients. They form relatively broad bands that overlap (Fig. 3.10). 

Penetrative hyphae can potentially play an important role in making the substrate accessible to enzymes [113]. On the basis of expected molecular diffusion coefficients of proteins in solutions of 10 m s enzymes would be expected to diffuse to depths of about 1 mm after 40 h, or even less if lower effective diffusion coefficients of around 10 m s occurred, such as might be expected within solid substrates [113]. Therefore enzyme diffusion occurs at a rate similar to hyphal penetration rates. As a result, the contribution of hyphal movement and release of enzyme from the hyphal tip would be significant in allowing the enzyme to reach greater depths than if the enzyme was simply released from the surface. Note that in modeling work to date enzyme release has been assumed to occur only at the interface between the substrate and biomass phases [84,85,114]. 

Young, M.E., Carroad, P.A., and Bell, R.L. 1980. Estimation of diffusion coefficients of proteins. Biotechnol. 

Unfortunately, some of the most basic aspects of the dynamics of adsorbed protein films are still unclear. For example, adsorption kinetics predicted by the bulk diffusion coefficient of proteins are usually too slow due to the existence of barriers to adsorption which may be entropic (orientational) or enthalpic (e.g. electrostatic in origin) [5]. This is important since diffusion of proteins to and from interfaces is generally much slower than with low molecular weight surfactants so that the contribution from bulk transport effects to changes in the stability may be enhanced. 

Techniques for Measuring the Diffusion Coefficient of Proteins in Hydrogels... 

Diffusion coefficients of proteins are often used as a measure of molar mass. For a spherical protein, D <= M" . Considering only one-dimensional diffusion, compare the fength of time it would take ribonuclease (M = 13.683 kg mol" ) to diffuse 10 nm to the length of time it would take the enzyme catalase (M = 250 kg mol" ) to diffuse the same distance. 

Table 3.A.5. Diffusion coefficients of proteins and other macromolecules in pure water at 20 C...

MUk is to be concentrated by ultraflltration in a hollow fiber module having the following dimensions and characteristics number of hollow fibers, 500 fiber internal diameter, 800 pm fiber length, 60 cm. The milk will flow on the tube side at an average flow velocity of 90 cm/s. The relevant properties of milk are viscosity, 0.8 cp density, 1.02 g/cm diffusion coefficient of proteins in milk, 6.5 x 10 cm /s milk protein contents, 2.8% w/v gel concentration Qgei, 25% w/v. 

Table 1.6. Lateral Diffusion Coefficients of Proteins Measured by Photobleaching (adapted from Cherry, 1979).

All values are average from two replicates Diffusion coefficient of proteins In water from the literature (Caspary, 1954 Nauman et al., 2007) Weight of protein released after 15 h of gel Incubatlon/welght of protein entrapped In the FAXMB gel. 

---