Glutamine determination

Furthermore, the response of this electrode was not disturbed when moderate concentrations of other amino acids were present. When determining glutamine in serum, a calibration curve with the same slope as of that in buffer was obtained, but owing to differences in viscosity of the sample from that of standard solutions, there was a slight shift along the potential axis. 

A hybridoma can live indefinitely in a growth medium that includes salts, glucose, glutamine, certain amino acids, and bovine serum that provides essential components that have not been identified. Serum is expensive, and its cost largely determines the economic feasibihty of a particular ciilture system. Only recently have substitutes or partial replacements for serum been found. Antibiotics are often included to prevent infection of the culture. The pH, temperature and dissolved oxygen, and carbon dioxide concentration must be closely controlled. The salt determines the osmotic pressure to preserve the integrity of the fragile cell. 

Since biosynthesis of IMP consumes glycine, glutamine, tetrahydrofolate derivatives, aspartate, and ATP, it is advantageous to regulate purine biosynthesis. The major determinant of the rate of de novo purine nucleotide biosynthesis is the concentration of PRPP, whose pool size depends on its rates of synthesis, utilization, and degradation. The rate of PRPP synthesis depends on the availabihty of ribose 5-phosphate and on the activity of PRPP synthase, an enzyme sensitive to feedback inhibition by AMP, ADP, GMP, and GDP. 

Blankenstein G., Preuschoff F., Spohn U., Mohr K.H., Kula M.R., Determination of L-glutamate and L-glutamine by flow-injection analysis and chemiluminescence detection comparison of an enzyme column and enzyme membrane sensor, Anal. Chim. Acta 1993 271 231-237. 

Figure 5 Five-channel enzyme sensor for the simultaneous determination of glucose, lactate, glutamate, glutamine, and ammonium. MFM, microfiltration module WV, valves P, pumps DC, dialysis cell B, blank reactors MC, reactor D, biosensor flow cell. (Adapted with permission from Ref. 34.)...

The first example of a dynamic flux analysis was a study performed in the 1960s [269]. In the yeast Candida utilis, the authors determined metabolic fluxes via the amino acid synthesis network by applying a pulse with 15N-labeled ammonia and chasing the label with unlabeled ammonia. Differential equations were then used to calculate the isotope abundance of intermediates in these pathways, with unknown rate values fitted to experimental data. In this way, the authors could show that only glutamic acid and glutamine-amide receive their nitrogen atoms directly from ammonia, to then pass it on to the other amino acids. 

R. Bischoff, H. V. J. Kolbe, Deamidation of Asparagine and Glutamine Residues in Proteins and Peptides Structural Determinants and Analytical Methodology , J. Chro-matogr., B 1994, 662, 261-278. 

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