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The Tautomerism of Quinones and the Question of Quinone Methide Intermediates in Oxidative Phosphorylation

From the ¹ From the Isotope Department, Weizmann Institute of Science, Rehovoth, Israel

A series of quinones, including vitamin K₁₍₂₀₎, have been shown not to exhibit isotopic hydrogen exchange. This finding is strong evidence against both the hypothesis of quinone methide tautomerism and the suggested occurrence of quinone methide intermediates in oxidative phosphorylation and various chemical reactions.

The results of previous studies on duroquinone with the use of nuclear magnetic resonance had been interpreted in terms of hydrogen isotope exchange in basic solution. This interpretation has been shown to be mistaken. The nuclear magnetic resonance results have now been shown to be due to the formation of a free radical in basic solution. The radical was also detected with the use of electron spin resonance spectroscopy.

The relevance of these results to the mechanism of oxidative phosphorylation is discussed.

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