Energy Coupling

Abstract

The ability of crude homogenates of animal tissues to catalyse oxidative phosphorylation with endogenous or added substrates was first reported by Kalckar in 1937. It later became apparent that the amount of phosphate esterified or ATP formed was stoichiometric with the amount of oxygen consumed. This stoichiometry is called the P/O quotient (or ATP/O quotient; mol. phosphate or ATP g-atom O⁻¹); its value reflects several parameters including the nature of the substrate undergoing oxidation, the integrity of the coupling membrane and the redox carrier composition of the respiratory chain. In the 1940s and early 1950s, workers in several different laboratories showed that the oxidation of NAD⁺-linked substrates such as 3-hydroxybutyrate or malate gave ATP/O quotients of approximately 3; similar values to these have subsequently been reported on many occasions, but there has been at least one claim that they are overestimated due to systematic experimental errors.