Fig. 1.

¹H-decoupled ¹³C nuclear magnetic resonance (NMR) spectrum of a heart extract. The working heart was supplied with a mixture of ¹³C-enriched long-chain fatty acids, ketones, lactate, pyruvate, and glucose in concentrations typical of a fed, rested animal. The multiplets of glutamate carbons 1–5, shown as insets, are the result of ¹³C-¹³C spin-spin coupling and reflect the relative rates of oxidation of these substrates. Ala, alanine; βHB, β-hydroxybutyrate; Lac, lactate; Ac, acetate; Suc, succinate; Asp, aspartate; Mal, malate; Cit, citrate; D, doublet; Q, quartet; S, singlet; T, triplet.