Sedimentation Velocity

In the case of a simple, homogeneous macromolecule, analysis of sedimentation velocity data provides s, the sedimentation coefficient, and D, the diffusion constant. Under favourable conditions, it is possible to extract s and D for mixtures of non-interacting macromolecular species, provided that boundaries for each species can be resolved or deconvoluted. The situation is more complicated for reversibly associating mixtures, since it is generally not possible to assign individual boundaries to discrete species.

A traditional method for analysis of sedimentation velocity experiments is to plot the natural logarithm of the boundary position versus time. The slope of this line is proportional to rn2s* where s* represents

Velocity Equilibrium

Velocity Equilibrium

Figure 4 Sedimentation velocity and equilibrium cell designs. (A) Two-sector velocity cell. Sample is loaded into the upper sector and reference solution (buffer) is loaded into the bottom sector. The sample is centrifuged at high rotational velocity, generating a boundary that moves towards the bottom of the cell. (B) Six-channel equilibrium cell. Three sample reference pairs are loaded into the cell, which is centrifuged at moderate rotational velocity, resulting in equilibrium concentration gradients in each sample channel.

Figure 4 Sedimentation velocity and equilibrium cell designs. (A) Two-sector velocity cell. Sample is loaded into the upper sector and reference solution (buffer) is loaded into the bottom sector. The sample is centrifuged at high rotational velocity, generating a boundary that moves towards the bottom of the cell. (B) Six-channel equilibrium cell. Three sample reference pairs are loaded into the cell, which is centrifuged at moderate rotational velocity, resulting in equilibrium concentration gradients in each sample channel.

an apparent average sedimentation coefficient. This approach does not provide information about the homogeneity of the sample or the diffusion constant. Consequently, a number of analysis methods have been developed that involve analysis of the entire boundary region. In 1978, van Holde and Weischet described a transformation procedure for removing the effect of diffusion from the boundary. It is particularly useful to determine homogeneity and to detect nonideal behaviour. More recently, Stafford described a time-derivative method for analysis of velocity data in which the time-invariant noise is removed by a subtraction procedure, resulting in a great increase in the signal-to-noise ratio. This approach is particularly useful in the analysis of data obtained with the interference optics, making it feasible to work at very low protein concentrations (e.g. 10-100 |g mL"1). Finally, there are methods for analysis of velocity experiments that involve directly fitting the scan data using either approximate or numerical solutions to the Lamm equation to determine both s and D. The Lamm equation is the partial differential equation that describes transport of solute(s) in the sector-shaped cells used in sedimentation velocity experiments. This approach can be used to fit data using single or multiple species models. Recently, Schuck has described a fitting algorithm which removes the radially-invariant and time-invariant noise contribution from the data, which makes this method particularly useful for data obtained with the interference optics.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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