Quinones

Quinones are redox molecules widely present in nature. Coenzyme Q is a subsituted benzoquinone having a polyprenyl chain in the 6-position (decaprenyl- in humans). It is a hydrophobic molecule imbedded in the lipid bilayer of mitochondria and other membranes; in mitochondria it is a component of the electron transfer chain and of the oxidative phosphorylation systems. In plant chloroplasts the function of Coenzyme Q is exploited by plastoquinone. Coenzyme Q in its reduced form is a potent antioxidant present in several membrane systems. Coenzyme Q is synthetized by animals starting from tyrosine; the isoprenoid side chain is synthetized through the mevalonate pathway. Among biological naphthoquinones are menaquinone, used for electron transfer in many bacteria, and Vitamin K, involved in the process of blood coagulation. Some o-quinones may be physiologically formed from cathecolamine derivatives. Substantial evidence exists that aminochromes and their chemical derivatives initiate deleterious effects at the cellular level that affect the supply of energy for the maintenance of vital cellular processes, particularly in the heart.