The inhibition of NADH oxidase by the lower homologs of coenzyme Q. |
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Authors: | G Lenaz P Pasquali E Bertoli G Parenti-Castelli |
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Affiliation: | Istituto di Chimica Biologien, Università di Bologna, 40126 Bologna, Italy;Institute for Biomedical Research, The University of Texas at Austin, Austin, Texas 78712 U.S.A. |
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Abstract: | The Coenzyme Q homologs having short isoprenoid chains are much less efficient than the higher homologs in restoring NADH oxidation in pentane-extracted lyophilized beef heart mitochondria; they have however high restoring activity for succinate oxidation. The same pattern is observed in pentane extracted submitochondrial particles ETP only if the quinones are added to detergent-treated membranes, showing that in ETP there is a decreased accessibility of the long chain quinones in comparison with the lower homologs. In intact mitochondria and ETP, CoQ3 inhibits NADH oxidation while leaving succinate oxidation unaffected; the inhibition of NADH oxidation by CoQ3 is not reversed by serum albumin but is reversed by CoQ7, particularly when the membrane has been previously “opened” with deoxycholate. CoQ3 may accept electrons from NADH in cyanide-inhibited ETP, allowing coupling at the first phosphorylation site as shown by the quenching of the fluorescence of atebrine. The mechanism of CoQ3 inhibition is probably related to its insufficient rate of reoxidation by the following segment of the respiratory chain when it has been reduced by NADH dehydrogenase. |
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