Membrane Stability

The enzymatic membrane was stored at 4 °C in buffer solution. Assays were performedatdifferent storagetimes. Figure29illustratesmembranestabil-itymeasured in the case ofPOD immobilization as the H2O2 concentration converted to purpurogallin, starting from a 5 X 10-5 M equimolar H2O2-

Fig.29. Enzyme activity (in %) of the POD-membrane (•) and catalase membrane (■) after storage at 4 °C in buffer solution. Activities were measured with hydrogen peroxide concentration of 10-3 M after circulation time of 20 min (flow rate: 1 ml min-1)

Time /day

Fig.29. Enzyme activity (in %) of the POD-membrane (•) and catalase membrane (■) after storage at 4 °C in buffer solution. Activities were measured with hydrogen peroxide concentration of 10-3 M after circulation time of 20 min (flow rate: 1 ml min-1)

pyrrogallol aqueous solution flowing across the membrane. In the case of catalase immobilization, the same operational stability with an initial H2O2 concentration of 2 x 10-2 M, was recorded. No significant decrease in enzyme activity was observed after 140 days and 8 h of cumulative dismutation reaction with a flow rate of 2 ml/min. The enzymatic membrane was remarkably stable compared to membranes made by other immobilization methods (Coche-Guerente et al. 1995; Cosnier 1999; Cosnier and Innocent 1993) and thus it should be noted that the enzyme was actually irreversibly immobilized. In the case of catalase immobilization, the stability is also satisfying; a loss of enzyme activity was only observed after 140 days of storage in buffer solution at 4 °C.

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