Ubiquinone restriction

The rates of the oxidative steps in the citric acid cycle are limited by the rate of reoxidation of NADH and reduced ubiquinone in the electron transport chain which may sometimes be restricted by the availability of O2. However, in aerobic organisms this rate is usually determined by the concentration of ADP and/or P available for conversion to ATP in the oxidative phosphorylation process (Chapter 18). If catabolism supplies an excess of ATP over that needed to meet the cell s energy needs, the concentration of ADP falls to a low level, cutting off phosphorylation. At the same time, ATP is present in high concentration and acts as a feedback inhibitor for the catabolism of carbohydrates and fats. This inhibition is exerted at many points, a few of which are indicated in Fig. 

Some patients on HMGCoA reductase Inhibitors (statins) experience muscle weakness. Secause the statins restrict the formation of ubiquinone, supplementation might be beneficial in some cases... 

Approaches such as those described above which rely on the isolation and detection of polyprenyl substituted phenols and quinones in lipid extracts are restricted by the minute quantities of compounds present and the difficulties, frequently encountered, in establishing a precursor relationship between the suspected intermediate and ubiquinone. Gibson and his colleagues approached the problem of ubiquinone biosynthesis in Escherichia coli K-12 by the isolation and examination of mutants unable to form ubiquinone. Five classes of ubiquinone deficient mutants were... 

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