Deciding on the Experimental System

To assess the validity of the analytical model developed for the basic system as well as of the results of pertinent numerical simulations, three experimental systems were investigated as model systems. These are presented below. 

The experimental system was selected based on the conclusions obtained from numerical simulations. Thus, in Section 4.1.4.1a it was found that to obtain an on/off output signal in a fed-batch reactor, the values of Vm,i and 

2 should be about 20 times the value of the largest Kmj value in the system. As such, relatively large amounts of enzymes are needed in each operation. (It should be pointed out that in the basic system, the two reactions take place simultaneously in the same medium and therefore the reaction conditions are not always optimal for both enzymes.) Thus, to examine the possibility of using the systems suggested above as experimental systems, the values of had to be determined for each of the substrates involved and under the experimental conditions actually employed. The results obtained are presented in Table 4.9. From these values the amounts of enzymes needed for each operation were estimated. 

From the results presented in Table 4.9 it can be seen that in systems 2 and 3, the substrates involved (i.e., glucose and ethanol) are characterized by high Km constants. High values for these substrates are also indicated in the literature. Only in system 1 do both reactions involve moderate values of Km,j and so can be operated with reasonable amounts of enzymes. Thus, system 1 was chosen to represent the basic system. 

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