Isotopic labeled fitly acid

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. 

Figure 3.21 Time courses of the hydrolysis of an isotopic quasi-racemate in two acid-catalysed hydrolyses of glycosides. Both figures, taken from Ref. 107, by kind permission of Prof. A. J. Bennet and the American Chemical Society, refer to a mixture of labelled d-sugar and unlabelled l-sugar (10mgmL each), show the least-squares best fit and display only every fourth data point for clarity, (a) Ring effect for methyl (3-xylopy-ranoside (b) anomeric effect for methyl 5-thio-oc-xylopyranoside. See Table 3.3 for numerical values of the effects, which are in opposite senses.

FIG. 5. Isotopic enrichment of urinary folate in an adult female subject during chronic ingestion of a low-folate diet supplemented with d2-folic acid. The value of 0.284 enrichment represents the labeling (i.e., isotopic enrichment) of ingested folate from dietary and supplemental sources. In this figure, the data were fit to the two-pool, one-output model depicted in Fig. 3, which yielded the solid regression line (Gregory el aL, 1994). 

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