Biomedical Engineering Reference
In-Depth Information
tiospecifities can be used to analyze the ratio ofenantiomers.Figure 9 shows the
principle of two different enantioselective biosensors. In the first method, one
sensor specifically detects a
D
-enantiomer whereas the second one analyzes the
concentration of a
L
-enantiomer.Method 2 shows a combination of an unspeci-
fic and a specific working sensor.Here,a comparison ofboth sensor signals allo-
ws a fast determination of the ratio of enantiomers.
Hundeck et al.(1993) showed the ET analyzing racemates of
DL
-phenylalanine-
methyl ester.Here,unspecific pig liver esterase cleaves both antipodes whereas
a
-chymotrypsin converts only the
L
-enantiomer (Fig. 10). Both reactions re-
lease protons that are easily detected by tris/HCl-buffer (enthalpy ofprotonation:
D
H = -47 kJ/mol).
Lammers (1996) extended the esterase/
-chymotrypsin system with
DL
-tryp-
tophan-,
DL
-tyrosine-,
DL
-methionine- and
DL
-phenylglycinemethyl ester. All
substances give very good signals with immobilized esterase and tris/HCl-
buffer. Immobilized
a
-chymotrypsin converts
L
-tryptophan- and
L
-tyrosine-
methylester with very good signals whereas
L
-methionine- and
L
-phenylglycine-
methylester effect only a few or give no heat. In contrast, the
L
-phenylglycine-
methylester seems to be too small for
a
-chymotrypsin, and
L
-methionine-
methylester is too hydrophilic due to its side chain (Lammers,1996).
a
4.2
Aminoacid Analysis
Aminoacid monitoring is of tremendous importance in biotechnology. In this
section, three different ET for
L
-arginine,
L
-asparagine and
L
-glutamine are
presented.The aminoacid
L
-arginine is required for an optimal growth and pre-
servation of nitrogen equilibrium.Moreover,
L
-arginine is important in hormone
producing processes (Alonso et al.1995).Thus,media for mammalian cell cul-
tivation such as Coon's F12 containing the aminoacids in relatively high con-
Fig.9.
Principles of enantiomeric analysis
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