Sedimentation velocity value

Equations suitable for simulation of molecular weight distributions for any initial distribution and chosen values of G(scission) and G(crosslinking) have been developed and demonstrated. The molecular weight distributions may be obtained by GPC (with the limitation of changes in relative hydrodynamic volumes) and by sedimentation velocity in the ultracentrifuge. 

Since the theories for the interpretation of sedimentation velocity experiments require the sedimentation coefficient at zero concentration, a series of experiments is performed at different concentrations. The value at zero concentration (or limiting sedimentation coefficient ), s[Pg.70]

Equation (3) shows that the sedimentation velocity increases with the density difference between the particle and the medium. Any situation that brings the density of the settling unit closer to that of the solvent will decrease the sedimentation velocity. To an observer who is unaware of its derivation, however, the smaller velocity would be interpreted by Equation (4) as indicating a smaller value of (m/f). Since the actual mass of colloidal material is unaffected by the solvation, it is more correct to attribute the reduced sedimentation velocity to an increase in the value of the friction factor. 

Some of the physicochemical parameters of the enzyme, as determined on the Kunitz preparation (S), are summarized in Table I. Sedimentation equilibrium analysis of molecular weight carried out on the enzyme crystallized from ammonium sulfate gave a value of 71,000 (5), in fair agreement with the value of 63,000 obtained by sedimentation velocity measurements on the Kunitz preparation (10). The enzyme has been reported to dissociate into subunits in the presence of sodium dodecyl... 

Figure 1.10 shows the velocities of deposition to a smooth surface of attached and unattached decay products, with a range of possible values of D. The scales are m s-1 for the attached and mm s 1 for the unattached decay products, illustrating the effect of attachment on diffusivity. For a nucleus of unit density with diameter, dp, equal to 0.17/um, the sedimentation velocity is 2 jum s 1, and deposition by Brownian diffusion and by sedimentation to upwards-facing surfaces are of comparable efficiency. For smaller particles, Brownian diffusion is always more effective. 

Lovenberg, Buchanan, and Rabinowitz 65) showed that the molecular weight of C. pasteurianum ferredoxin is about 6000, based on sedimentation velocity and sedimentation equilibrium ultracentrifugation determinations and on amino acid analysis. The sedimentation coefficient, S2o,w was 1.4, and the partial specific volume, determined according to the method of Hvidt et al. 59) was 0.63, as compared to the value of 0.71 observed for most proteins. Similar investigations showed that ferredoxins from four other clostridia Lovenberg, Buchanan, and Rabinowitz 65)) and from a photosynthetic bacterium (Bachofen and Arnon 12)) also had a molecular weight of about 6000. 

Physical measurements support a molecular weight of approximately 200,000. This value is also in accord with gel exclusion studies on Sephadex G-200. Thus the enzyme contains 1 mole of flavin and 4 g-atoms of nonheme iron per mole.. . . The sedimentation velocity of the beef heart enzyme at 10-15 mg protein/ml is 6.5 S. . . This preparation could oxidize succinate in the presence of ferricyanide or phenazine methosulfate (PMS) as electron acceptor but was unable to transfer elec-to be unable to interact with the respiratory chain. 

Using the sedimentation velocity procedure, Stamm found the average degree of polymerization of purified cotton linters dispersed in cuprammonium hydroxide solution to be 346. It was subsequently shown by Svedberg, however, that reliable values for the diffusion constant could not.be obtained in the ultracentrifuge and consequently the results of Stamm are probably in error. 

The viscosity of the liquid phase is an important consideration. It is a known fact that the sedimentation velocity and the filtration rate vary inversely as the viscosity of the suspending liquid. Temperature, purity, and the amount of dissolved solids materially affect the viscosity value therefore, it is essential that direct measurement of viscosity be made on the solid-liquid system. 

Figure 4. Sedimentation Velocity Analysis of ZDD. A, Primary data collected at 1 mg/ml (10 scans). B, Apparent sedimentation coefficient distribution function, g(s ) versus s. The error bars represent the standard error of the mean. The solid line is the fit to equation 4. Apparent s, D, and Ms,D values were calculated as described.

The porosity of the flocculated suspensions in the experiments is always smaller than 0.005. This value is measured with a Malvern Particle Sizer type 2200 when very high coagulant doses were used. Therefore, the correction for the sedimentation velocity is always smaller than 1.02. 

Thus, Eq. (16), together with the data from Table 1, predict an observable contribution of surface phenomena to the particles sedimentation velocity for all the types of surface interaction, except the van der Waals interaction. The possible values of criterion Rel range from about 1000 h 10 cm and eq = 5) to about 2000 (h 10 cm and eq = 10). 

When used properly, ultracentrifugation continues to be our major means of determining molecular weight values for humic substances using sedimentation velocity and other techniques. Indeed, centrifugation studies with humic substances have usually centered upon molecular weight measurements. 

Results for the Whatman 541 filter paper (23-28), flat plates (14-22), and Petri dishes (31,32) are shown in figures 7, 8, and 9 respectively. The data for the filter paper and flat plates have been presented as separate points for each measurement reported in the literature. For the Petri dishes, only the mean values and standard errors were available. Least squares regression lines plotted through the points are also shown. Figure 10 presents all three regression lines plotted on the same axes with the predicted sedimentation velocity line. It must be cautioned that a comparison of the regression lines is tenuous due to the spread in the data represented by each line. 

For more concentrated suspensions (q> >0.2), the sedimentation velocity becomes a complex function of At > 0.4, a hindered settling regime is usually entered whereby all of the particles sediment at the same rate (independent of size). A schematic representation for the variation of v with is shown in Figure 9.12, which also shows the variation of relative viscosity with rp. It can be seen from these data that v decreases exponentially with increase in approaches zero when cp approaches a critical value (the maximum packing fraction). The relative viscosity shows a gradual increase with increase in cp such that, when cp = the relative viscosity approaches infinity. 

The dissociation of apoferritin at extremes of pH was examined by sedimentation velocity techniques (166). It was established that between pH 2.8—10.6 the apoferritin monomer ( 17S) was the only species that could be detected. Between pH 2.8—1.6 and 10.6—13.0 both monomer (17S) and a low molecular weight component (2—3S), presumed to be subunit, were detected. The dissociation follows a smooth sigmoidal curve (Fig. 7 a) in both cases with mid points, corresponding to equal amounts of 17 S and 2—3S component at 2.2—2.4 for the acid dissociation and 11.8—12.2 for the alkaline dissociation (the exact values are dependent on the buffer used). When apoferritin is completely dissociated into subunits at low pH (either by exposure to buffer of pH 1.6, or by treatment with 67% acetic acid) and is then dialysed into buffer of higher pH, reassociation does not take place in dilute glycine buffers until pH values in excess of that required to induce subunit dissociation (Fig. 7 a). The reassociation then follows a sigmoidal curve until complete reassociation to a 17S monomer is attained at pH 4.3. Although we have not as yet been able to follow reassociation completely in a more concentrated buffer (200 mM cf 10 mM) it is clear (Fig. 7 a) that subunit reassociation occurs at a much lower value and that the hysteresis observed between dissociation and reassociation is much less in the more concentrated... 

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