Changes in the pH-Activity Profiles of Enzymes upon Immobilization on Polyelectrolyte-Containing Hydrogels

Understanding changes in the physicochemical properties of enzymes upon immobilization is the key to optimizing their activities. Immobilization on or modification with polyelectrolytes will induce shifts in the pH-activity profiles of enzymes, but a systematic study comparing various enzymes and polyelectrolyte supports is lacking. Here, we report the pH-activity profiles of eight enzymes immobilized via covalent bonds within six different polyacrylamide-<i>co</i>-polyelectrolyte hydrogel particles containing diverse ionic groups. Depending on the enzyme, shifts of the maximum activity toward either acidic or basic pH, as well as broadening of the pH-activity curves, were observed. While a general correlation of the direction of the shifts with the nature of the polyelectrolyte is not evident, we highlight that enzyme structural features, electrostatic factors, and local buffering are among the determinants of the observed effects. Finally, we demonstrate examples of unexpectedly large shifts that can be used to create biocatalysts with improved activities at unusual pHs.