Review Article

Identifying Sources of Hepatic Lipogenic Acetyl-CoA Using Stable Isotope Tracers and NMR

Figure 3

Schematic depicting determination of the acetyl-CoA precursor 13C-isotopomer pattern from 13C NMR analysis of the terminal and penultimate carbon resonances with prior knowledge of the fraction of newly synthesized palmitate. In this example, 10% of palmitate was newly synthesized. The methyl ester (–OCH3) signal is an intramolecular natural abundance standard representing 1.1% 13C-enrichment. The 13C palmitate multiplet signals are decomposed into contributions from 13C-enriched acetyl-CoA isotopomers and background 13C. Acetyl-CoA that is not derived from enriched 13C-precursors (shown in light grey) has a 1.1% background 13C-enrichment. Its contribution is calculated as the difference between the newly synthesized fraction (10%) and the sum of the 13C-enriched acetyl-CoA isotopomers (5%). Since 10% of the palmitate was newly synthesized, the precursor acetyl-CoA isotopomer enrichments are 10 times that of the palmitate 13C-isotopomers.
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