The currents of life: The terminal electron-transfer complex of respiration

Aerobic organisms derive most of the energy needed for life processes by the burning of foodstuffs with the molecular oxygen in air, as first suggested in 1789 (1) by Antoine Lavoisier (1743-1794). In the first part of the respiratory process, hydrogen atoms are extracted from organic molecules. The hydrogen carriers are later regenerated in the respiratory chain located in cell organelles, mitochondria, or, in bacteria, in the cell membrane. These chains consist of a series of membrane-bound protein complexes in which the hydrogen atoms are split into protons and electrons. The electrons are passed down the chain and reduce molecular oxygen to water, whereas the protons are left behind on one specific side of the membrane. In addition, the electron transfer (ET) or "current" through the chain is coupled to a pumping of additional protons from water to the same membrane side. Thus, the two proton currents lead to an increased positive charge and decreased pH on this side-i.e., an electrochemical potential across the membrane, analogous to a storage battery. This potential drives the synthesis of ATP, the universal energy currency in living cells, by a chemiosmotic mechanism formulated by Peter Mitchell (2), who was awarded the Nobel Prize in Chemistry in 1978