Enzyme Reactor with Simple Kinetics

A bioreactor is a device within which biochemical transformations are caused by the action of enzymes or living cells. The bioreactor is frequently called a fermenter6 whether the transformation is carried out by living cells or in vivo7cellular components (that is, enzymes). However, in this text, we call the bioreactor employing enzymes an enzyme reactor to distinguish it from the bioreactor which employs living cells, the fermenter. 

7 Literally, in life pertaining to a biological reaction taking place in a living cell or organism. 

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Enzyme linked electrochemical techniques can be carried out in two basic manners. In the first approach the enzyme is immobilized at the electrode. A second approach is to use a hydrodynamic technique, such as flow injection analysis (FIAEC) or liquid chromatography (LCEC), with the enzyme reaction being either off-line or on-line in a reactor prior to the amperometric detector. Hydrodynamic techniques provide a convenient and efficient method for transporting and mixing the substrate and enzyme, subsequent transport of product to the electrode, and rapid sample turnaround. The kinetics of the enzyme system can also be readily studied using hydrodynamic techniques. Immobilizing the enzyme at the electrode provides a simple system which is amenable to in vivo analysis. 

In the following sections the extension of Eq. (18) to more complex reaction schemes is described. Again the rapid equilibrium assumption is used to show how more complex rate equations are derived from simple Michaelis-Menten kinetics. Attention is focused on some typical rate equations that are useful to describe enzyme kinetics with respect to a desired process optimization. The whole complexity of enzyme kinetics is of importance for a basic understanding of the enzyme mechanism, but it is not necessary for the fitting of kinetic data and the calculation of reactor performance. 

Once ku has been experimentally determined (see section 3.5.2), the curve of reactor operation (X vs t) can be obtained for a certain enzyme concentration (meat)-Eq. 5.69 also allows reactor design (determination of reactor volume), since meat is simply the ratio of enzyme load to reaction volume (Mcat/VR). Simulation of batch bioreactor operation under different scenarios of enzyme inactivation is presented in Fig. 5.16 for simple Michaelis-Menten kinetics (a = 14-K/Si b = -1 c = 0) with Si/K =10. Enzyme load in the reactor was calculated to obtain 90% conversion after 10 h of reaction under no inactivation. The strong impact of enzyme inactivation on bioreactor performance can be easily appreciated. 

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