Diffusion coefficients for protein molecules in blood serum.

A new technique is described for the measurement of the self-diffusion coefficients of protein macromolecules in solution. The method makes use of the phenomenon of Taylor dispersion of a solute introduced into a solvent flowing in the laminar regime through a tube of circular section. Results are reported for the self-diffusion coefficient of cholesterol associated with lipoprotein molecules in dogs' serum at pH 7.4 in the temperature range 18-37 degrees C. The diffusivity of bovine serum albumin in serum has also been studied as a function of temperature at pH 7.4 and 4.7. In the more basic solution, measurements of the diffusivity as a function of protein concentration substantially agree with earlier work. For all the systems studied the diffusivity varies rapidly with temperature. The pH of the solution, in the case of bovine serum albumin, also has a significant effect on the diffusivity of the macromolecule. The latter observation is related to the amount of water bound to the protein molecule in solution.