Loss of activity or gain in stability of oxidases upon their immobilization in hydrated silica: Significance of the electrostatic interactions of surface arginine residues at the entrances of the reaction channels

The structural origin of the extreme variation of the effect of silica sol-gel immobilization on the stability of flavoprotein oxidases is examined. In glycolate oxidase and lactate oxidase, highly conserved positively charged arginine surface residues guide the substrate anions into channels containing the active sites. In glucose oxidase, both positively and negatively charged (arginine and aspartic acid) residues are found at the channel opening. We postulate that electrostatic interaction between the positively charged residues in lactate and glycolate oxidases and polysilicate anions disrupts the function or structure of these alpha-hydroxy acid oxidases upon their immobilization in hydrated silica. Such damaging interaction does not occur in glucose oxidase where the surface charges are internally balanced. The damaging electrostatic interactions of the alpha-hydroxy acid oxidases are avoided, and the enzymes are stabilized instead of being deactivated when complexed with polycations, prior to their immobilization in hydrated silica.