Mitochondrial uncoupling and the isodynamic equivalents of protein, fat and carbohydrate at the level of biochemical energy provision.

The effects of uncoupling of mitochondrial oxidative phosphorylation on the efficiency of energy conservation during oxidation of amino acids, fatty acids, glycerol, glucose and 101 food proteins have been examined in order to compare how uncoupling at coupling site 1 affects energy yields compared with uncoupling at sites 2 + 3 and uncoupling by proton leakage. The effects of uncoupling by each mechanism on the isodynamic equivalents of carbohydrate, fat and protein at the level of cytoplasmic ATP yield have been estimated. Energy conservation during amino acid oxidation decreased relative to that for glucose as uncoupling by all three mechanisms increases. This effect is least when uncoupling is at site 1 and is associated with a fall in the isodynamic equivalent for protein:glucose of 4% maximally, and a fall in the cytoplasmic ATP yield for glucose of 25% (15-30%) when accounting for uncertainty in the choice of proton stoichiometries). Variation in the efficiency of energy conservation for the different amino acids is large for both highly coupled and uncoupled mitochondria but the range of efficiencies for the oxidation of 101 food proteins is relatively small (less than 6% of the mean) for a tightly coupled system. This range increases absolutely (minimally fourfold) and relatively (minimally 44% of the mean value) with severely uncoupled mitochondria but is nearly constant (changes by less than 1% relative to the mean) within the probable physiologically relevant range of uncoupling in the whole body and in the full range of uncoupling at site 1.(ABSTRACT TRUNCATED AT 250 WORDS)