Plasma membrane coenzyme Q10 and growth control

Coenzyme Q is distributed among cellular membranes and it has a significant concentration at the plasma membrane. The plasma membrane contains a trans-membrane electron transport system, which is centered on coenzyme Q. This molecule is maintained reduced by NAD(P)H-dependent enzymes and can reduce other antioxidants such as tocopheroxyl quinone and ascorbate free radical. Its antioxidant property and its ability to maintain in the reduced state the other antioxidants offers a system to protect membrane components against oxidations and prevents oxidative-stress-dependent cellular damage. Growth factor withdrawal induces cell growth arrest and apoptosis through an oxidative-stress-induced pathway. Coenzyme Q can stimulate growth of different cell lines under serum deficiency, mainly by preventing apoptosis. The protection caused by coenzyme Q is independent of the Bcl-2 protein. Plasma membrane coenzyme Q appears to be essential in the regulation of the redox equilibrium of the cell and redox-dependent pathways.