The essentiality of coenzyme Q for bioenergetics and clinical medicine

Coenzyme Q is an essential component of the respiratory chain, where it represents a mobile pool between dehydrogenases and cytochromes. The fact that Q is a free component, and its concentration is not in great excess over the Km of the respiratory complexes, renders this compound potentially rate-limiting in the respiratory chain. On the other hand, the rate of lateral diffusion of Q in the mitochondrial membrane is not a limiting step under physiological conditions. Quinoid compounds, which act as inhibitors of the respiratory chain at the level of Q, besides being useful tools for investigations of electron transfer, could be important in pathology as inhibitors of respiration.