STABILIZATION OF GLUCOSE-DEHYDROGENASE WITH POLYETHYLENEIMINE IN AN ELECTROCHEMICAL REACTOR WITH NAD(P)(+) REGENERATION

The stability of the enzyme glucose dehydrogenase (GDH) has been studi ed under turnover conditions in an electrochemical reactor with NAD(P) (+) regeneration on a preparative scale. The enzyme showed first-order deactivation patterns closely related to imposed potential. An increa se in the applied potential caused a decrease of the half-life deactiv ation time of the enzyme (t(1/2)). However, this detrimental effect wa s compensated with an enhancement of the substrate consumption rate (r (s)) attained as a consequence of the higher cofactor regeneration rat es observed at more positive potentials. A 0.7 V potential (vs Ag\AgCl ) was selected as a compromise between the activity and the stability of the enzyme (t(1/2) = 4.2 h; r(s) = 32 mu mol min(-1)). The protecti ve effect on the activity of glucose dehydrogenase of well-known stabi lizing agents such as NaCl, sorbitol, bovine serum albumin (BSA) or po lyethyleneimine (PEI) has been studied. PEI(50 000 MW) at concentratio ns between 0.3 and 0.5 mM showed the highest protection of the enzyme activity in the electrochemical reactor as well as the highest substra te consumption rates (t(1/2) 24.5 h; r(s) = 59 mu mol min(-1)). This b eneficial effect of PEI is explained in terms of an electrode, cofacto r, and enzyme modification that induces an increase of the concentrati ons of NAD(P)H and glucose dehydrogenase in the vicinity of the electr ode and minimizes the adsorption of the enzyme on the electrode contac t.