Thermal Biosensors in Biotechnology - Advances in Biochemical Engineering Biotechnology - page 55

time measurements at hospitals. Moreover, patients individual urea level and
ureases long term stability encourages one to employ the method in routine
treatment.
4.4
Kinetic Characterization of Immobilized Biocatalysts
Immobilized enzymes are not restricted to bioanalytical applications.Increas-
ingly they attract a huge amount of interest in industrial organic chemistry due
to their excellent stereo- and enantioselectivity.Moreover,they work under mild
conditions of temperature, pH and pressure. Therefore, the determination of
kinetic constants is of great interest. They allow quantitative characterization
of immobilized biocatalyst preparations and facilitate comparisons between
different materials and procedures for biocatalyst immobilization.
Stefuca et al.(1990) proposed an ET method offering a rapid,convenient,and
general approach to determine kinetic constants of immobilized biocatalysts.
Here, a differential reactor (DR) was used for the measurement of the initial
reaction rate ofsucrose hydrolysis (Vallat et al.1986).The enzyme column ofthe
ET has been considered as a differential packed-bed reactor,and with a mathe-
matical model,intrinsic kinetic constants of immobilized invertase were calcu-
lated from experimental DR and ET data.
Recently,the method was used to estimate kinetic constants of immobilized
invertase in a column with different conjugates of concanavalin A (Docolo-
mansky et al.1994).The immobilization is based on a strong biospecific glyco-
protein-lectin interaction.Due to its reversibility,this immobilization procedure
is of huge interest in enzyme technology. Exhausted glycoenzymes are easy to
exchange by fresh biocatalysts (Saleemuddin and Husain,1991).
Gemeiner et al.(1993) presented a similar method for the direct determinati-
on of catalytic properties of immobilized cells. Cephalosporin C transforming
Trigonopsis variabilis were immobilized by three different methods,filled into a
column and set into the ET.After thermal equilibration,Cephalosporin C solu-
tions (0.1-50 mmol/l) were continously pumped through the ET until steady-
state heat production was obtained.Again,the ET was shown to be suitable for a
rapid and simple estimation of the kinetic properties of immobilized cells.
Microkinetic factors such as mass transfer were taken into account (Stefuca et al.
1994). Thus, ET measurements allow us to obtain intrinsic data, even from
immobilized cells. Moreover, the data can be applied to optimize biocatalyst
design and bioreactor models (Gemeiner et al.1996).
4.5
Monitoring of Enzyme Catalyzed Syntheses
During the last decade, the role of enzyme catalysis in organic chemistry has
increased tremendously. The availability of a huge variety of enzymes, the
willingness of chemists to use them even in non-aqueous reaction phases and
progress in immobilization techniques and bioreactor design led to a number of
applications in bioorganic chemistry.Biosensors might be an interesting moni-