Fig. 1.

Representative ¹³C NMR spectra of perchloric acid extracts of hearts perfused with and without four different concentrations of [1-¹³C]sodium propionate (indicated in the figure). [1,6-¹³C]glucose (5.6 mM) and uniformly ¹³C-enriched free fatty acids (0.63 mM) were also present in the perfusate. Resonances corresponding to C4 of glutamate (~34.5 ppm) and C3 of aspartate (~37.5 ppm) are shown. Insets i and ii show the spectral components for each metabolite. S is singlet, D is the doublet assigned to the coupling indicated in each subscript, and Q is the quartet, actually a doublet of doublets associated with isotopomers that have three consecutive carbons enriched in ¹³C. Aspartate C3 shares the same atom mapping as glutamate C4 and hence reports on acetyl-CoA labeling in an analogous manner.