Investigation of Catalytic Properties of Immobilized Enzymes and Cells by Flow Microcalorimetry - Advances in Biochemical Engineering Biotechnology - page 71

Fig. 2. Steady-state heat response measurement for different input substrate concentrations

the enzyme reaction released in the column (standard dimensions of the packed
bed are 2 cm length and 0.4 cm inner diameter). The column is operated as a
packed bed reactor. At the beginning of experiment the system is stabilized by
pumping a buffer solution through the column. After thermostating, the mea-
surement is begun by replacing the buffer with the substrate solution.
The most common procedure is pumping a substrate solution of a defined com-
position (concentration of substrate and other compounds having influence on the
enzyme activity) through the microcalorimetric column. The basic information
provided by the microcalorimetric measurement is the relation between reaction
conditions and the steady-state heat response, T r ,measured as the temperature

difference between the column input and output. Figure 2 is an illustration of
such measurement.In the next part of this review,the mathematical assessment
of the experimental data,based on mass and heat balances,is provided.

D

3
Heat and Material Balance

The value of a thermometric signal is calculated by means of a mathematical
formulation of the heat and material balance in the reaction system,represented
by the microcalorimetric column packed with an immobilized enzyme. The
microcalorimetric column with an IMB can be defined as the continuous packed
bed reactor depicted in Fig. 3.The balance equations were derived according to
the following simplifying assumptions,which had been previously verified [27]:
- changes of the substrate concentration and temperature along the reactor
are so small that the reaction rate, the molar reaction enthalpy and the fluid
specific heat capacity are constant,
- plug flow occurs in the reactor;
- the flow rate is sufficiently high to prevent reaction-rate limitation by external
mass transfer,
- heat losses from the reactor are neglected and the reactor is considered to be
adiabatic.