Effect of Charge on Protein Diffusion in Hydrogels

Abstract

To study the effect of charge on protein diffusion in hydrogels, mutual diffusion of a globular protein, myoglobin, has been investigated at various pH and ionic strength levels in two kinds of polysaccharide gels, neutral agarose gel and anionic carrageenan gel, by the recently developed electronic speckle pattern interferometry method. In the uncharged agarose gel, diffusions of myoglobin are not effected by the change in pH and the ionic strength, indicating no electrostatic interaction between the gel and myoglobin. The experimental data in agarose gel agree with the combined model proposed by Clague and Philips for the diffusion of spheres in hydrogels. While in the negatively charged λ-carrageenan gel, the diffusion of myoglobin is accelerated by electrostatic attraction when the pH is lower than the isoelectric point (pI) of the protein, but it is extensively hindered by the electrostatic repulsion when pH > pI. The diffusion of myoglobin in λ-carrageenan gel agrees with the Tsai and Strieder model to give an apparent radius of the protein at various pH values.