In the great majority of biochemical and biophysical textbooks, the proton-motive respiratory chain inherent in mitochondria and respiring bacteria is erroneously presented. Usually the initial, middle, and terminal segments of the respiratory chain are shown as old-fashioned Mitchellian loops (e/H+ antiports), whereas the experimentally proved Mitchellian Q-cycle is omitted. As a result, both the mechanisms and H+/e stoichiometry of respiratory energy transductions appear to be wrong. Such a situation looks especially bad if we take into account that the respiratory chain provides the main portion of energy required to synthesize the 40 kg of ATP that is formed by an adult man each day. Some of the above mistakes can also be found in the original version of the D. Nicholson §1 metabolic map published in our journal in 2001 [1].

The revised version of the same map that is published here (Fig. 1) is correct and for certain will be useful for both lecturers and students dealing with bioenergetics. Nevertheless, some comments are required.

  • To simplify the scheme, D. Nicholson presents Q-cycle as a mechanism where the high potential heme bH12 always reduces both UQ and UQ˙ to form UQH2. On the other hand, it is already clear that one electron for UQ reduction can be supplied by NADH dehydrogenase (Complex I) and another by bH.

  • It is not indicated that the ATP/ADP antiport through the inner mitochondrial membrane is electrophoretic (exchange of ATPin4− for ADPout3−) being driven by the electric potential difference (inside negative) across this membrane (ΔΨ). The ΔΨ formation by the respiratory chain is not shown in the scheme and not mentioned in the legend.

  • GTP formed when succinyl-CoA is converted to succinate is not obligatorily used to form ATP as shown in the map. For example, it can be utilized inside mitochondria by mitochondrial ribosomes when proteins encoded by mitochondrial DNA are synthesized.

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Figure FIGURE 1..  

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  • 1

    School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom

  • 2

    The abbreviations used are: bH, high potential heme b; UQ, ubiquinone.


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