Diffusion of lysozyme in gels and liquids - A general approach for the determination of diffusion coefficients using holographic laser interferometry

A study on diffusion measurements of the protein lysozyme in liquids and ag arose gels, at different pH and ionic strengths, has been performed using h olographic laser interferometry. The measurements showed that the diffusive flux was very dependent on pH and ionic strength when the protein was not at its isoelectric point or when the charge of the lysozyme molecules was n ot screened by ions in the solution. Evaluation of the experimental data wi th Fick's law, resulted in diffusion coefficients for lysozyme that are str ongly dependent on pH and ionic strength. Evaluation of the experimental da ta using a more general transport model, based on chemical potential gradie nts instead of concentration gradients resulted in lysozyme diffusion coeff icients that are independent of pH and ionic strength. The chemical potenti al was estimated by using the Poisson-Boltzmann equation. (C) 2000 Elsevier Science B.V. All rights reserved.