Ubiquinone Coenzyme formation

In addition to succinate, malonate, fumarate, and phosphate, it has been reported in recent years that succinate dehydrogenase is activated by ATP, ITP, IDP (195), reduced ubiquinone-10 (195-197), succinyl coenzyme-A (198), formate, ClOr, I", Br-, C1 , NOa, SO4 ", acid pH... 

In system (6) peroxidation of membrane lipids can be initiated not only by ubiquinone, but also by nicotinamides. This can be explained if one bears in mind that, as can be seen from reaction (3), redox equilibrium between the oxidized and reduced forms of coenzymes is accomplished through intermediate stages at which radicals are formed. For instance, NADH is not oxidised immediately to NAD+ but passes through the stages of formation of NAD or NADH+. Since nicotinamide does not penetrate into the membrane phase, it itself cannot cause oxidation of hydrocarbon residues of fatty acids, it could be supposed that NADH initiated peroxidation through peroxide anions O2, which can be formed according to the following reaction ... 

Scheme 11.86. A brief representation for the formation of ubiquinone from chorismate. The compound ubiquinone or coenzyme Q occurs as different variants depending on the length of the isoprenoid side chain. As its name implies, it is (they are) ubiquitious and not all steps are known in its biosynthesis.

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