Fig. 2.

Influence of pyruvate concentration ([pyruvate]; [Pyr]) on the carbon-4 resonance of glutamate. These ¹³C spectra were acquired from hearts exposed to the “fed” mixture of substrates at graded [pyruvate], 0.12 mM (bottom) or 1.0, 3.0, and 6 mM (top). The fraction of acetyl-CoA derived from pyruvate relative to the fraction from long-chain fatty acids is indicated by the ratio (S + D34)/(Q + D45). At 3 mM pyruvate, the oxidation of long-chain fatty acids is inhibited. F, resonances arising from oxidation of ¹³C-enriched long-chain fatty acids; P, resonances arising from oxidation of ¹³C-enriched pyruvate, Q, quartet due to J₄₅ and J₃₄ coupling; D34, doublet due to J₃₄ coupling; D45, doublet due to J₄₅; S, singlet due to glutamate with ¹³C in position 4 but not position 3 or 5. J is standard notation for the spin-spin coupling constant.