Figure 6

Stability of Tv DAO immobilized on Sepabeads EC-EP in repeated batches of D-Met conversion. Oxidative deamination of the substrate (20 mM initial concentration in 20 mL Tris-buffer) was done in a stirred reactor (300 rpm) at 30°C with aeration at 15 L/h. Panel A shows a typical time-course of the concentration of dissolved oxygen during one batch of D-Met conversion. The inset illustrates the determination of enzymatic activity at the beginning of each batch from initial rates of oxygen consumption (dotted line) after addition of the substrate. Aeration was turned off for the measurement and turned on again when the level of O₂ had dropped below 100 μM, which is marked by an increase of the signal. Panel B shows the operational stability of the immobilized enzyme and compares the three methods to calculate the residual activity in every batch: initial rate measurements (triangles); the average oxygen concentration as long as D-Met is not limiting (diamonds); and the reciprocal of the total batch time (open squares). The solid line is a straight-line fit to the averaged data from all three methods.