Table 3

Fuel energetics of various substrates

SubstrateP/O ratio***Energy liberated, kcal/mol of 2-carbon units
Glucose2.58223.6
Pyruvate2.50*185.7*
Palmitate2.33**298**
BHOB2.50*243.6*
  • *Although the difference in energy produced by BHOB (per oxygen atom consumed) is comparable to pyruvate, more energy is derived from BHOB vs. pyruvate due to BHOB being more reduced. If pyruvate were burned in a bomb calorimeter, it would liberate 185.7 kcal/mol of 2-carbon units, whereas the combustion of BHOB would liberate 31% more calories (243.6 calories/2-carbon unit).

  • **Combustion of palmitate generates 298 kcal/mol of 2-carbon units, but there is loss of ATP due to uncoupling proteins generating heat instead of ATP.

  • ***P/O ratio reflects the number of molecules of ATP produced per atom of oxygen reduced by the mitochondrial electron transport chain.