Thermal Biosensors in Biotechnology - Advances in Biochemical Engineering Biotechnology - page 51

Fig.10. Enantiomeric analysis of DL -phenylalaninemethylester
centrations (2 mmol/l and higher). The analysis of L -arginine is performed
using coimmobilized arginase (1000 units) and urease (250 units) in 0.1 M
potassium phosphate buffer pH 9.5.Due to the instability of urease,the buffer
contains 2 mm L -cysteine as well.Arginase cleaves the aminoacid to L -ornithine
and urea. Consequently, urease converts the urea to ammonia and carbon di-
oxide. The sequential amplification reaction showed a broad detection range
(0.1-100 mmol/l) similar to immobilized urease columns. This might be ex-
plained by similar Michaelis-Menten-values (arginase:K M =11.6 mmol/l;urease:
K M =10.5 mmol/l).The amplification factor is about fourteen.
The aminoacid L -asparagine is used as a nitrogen source in different cultiva-
tion processes.Especially,the aminoacid L -asparagine has found application in
fermentation processes of ergotamine-producing Claviceps purpurea .Here,
medium concentrations up to 10 g/l are used (Amici et al.1967).The ET is set up
for L -asparagine analysis by columns of immobilized aparagine (200 units).
Asparagine deaminates the aminoacid and give good signals in the range
0.5 and 100 mmol/l. The best signals were obtained in 0.1 M potassium phos-
phate buffer at pH 8.6.Nevertheless,the system works in 0.05 M Tris/HCl as well.
The latter might be interesting for samples with high magnesium content.In this
case,potassium phosphate buffer is not suitable because magnesium phosphate
causes problems in FIA-systems.
Especially in mammalian cell cultivations, the aminoacid L -glutamine and
glucose represent the most important energy sources.The aminoacid is carbon
and nitrogen source for the syntheses of aminoacids,fats,proteins,antibodies,
nucleotides,purines and pyrimidines (Jeong and Wang,1995).Thus,monitoring
of L -glutamine is a desirable task.An ET employment is possible with coimmo-