Question

A scientist is worried that the mitochondria he is studying are uncoupled. They estimate high rates of the electron transport chain activity by measuring NADH oxidation, high rates of oxygen uptake using a Clark electrode, but very low ATP synthesis in an assay. Explain what is happening in the experiment and assess their analysis - are they right?

Answer 1

High rate of NADH oxidation means the Electrons are transferred through the ETC complexes very efficiently. But it is observed that ATP is not forming. It may happen due to some process such as basal proton leak, electron leak and electron slip phenomenon. But as oxygen uptake and its conversion to water is normal, electron leak and electron slip is not occuring. If electron are leaked or escaped in any way, oxygen will not be converted into water as oxygen is the terminal electron acceptor molecule. The incident which is occuring here in the uncoupled mitochondria is basal proton leakage. Protons can directly escape from the inner mitochondrial space by diffusion through the inner mitochondrial membrane, a process named basal proton leak.

At normal condition in ETC, protons are moved from mitochondrial matrix to inner membrane space while transporting of electrons through various complexes of ETC, located in the inner mitochondrial membrane. These protons move back to mitochondrial matrix through ATP synthase enzyme and during this transport, ATP is synthesized from ADP. But if due to leakage, protons moves inside the matrix without the aid of ATP synthase enzyme, then ATP will not be synthesized or will be synthesized at very low rate s is happening here.