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Difference between revisions of "Talk:Chicco 2022 MitoFit"

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:::: Abstract: 'under S- and some N+S pathway states, rotenone elicits a paradoxical increase in ''J''<sub>O<sub>2</sub></sub>, ..'
:::: Abstract: 'under S- and some N+S pathway states, rotenone elicits a paradoxical increase in ''J''<sub>O<sub>2</sub></sub>, ..'
::::::* In the S-pathway state (without rotenone), an increase of ''J''<sub>O<sub>2</sub></sub> elicited by rotenone is by no means paradoxical, but is classically expected, if oxaloacetate β€” accumulating in mitochondria without malate-anaplerotic capacity β€” can leak out of the mt-matrix such that its concentration is lowered after inhibiting its production by rotenone through redox-coupled NADH (product) inhibition of MDH.
::::::* In the S-pathway state (without rotenone), an increase of ''J''<sub>O<sub>2</sub></sub> elicited by rotenone is by no means paradoxical, but is classically expected, if oxaloacetate (inhibitor of CII) β€” accumulating in mitochondria without malate-anaplerotic capacity β€” can leak out of the mt-matrix such that its concentration is lowered after inhibiting its production by rotenone through redox-coupled NADH (product) inhibition of MDH.


:::: Introduction: 'monitoring the effect of selective CI or CII substrates ..'
:::: Introduction: 'monitoring the effect of selective CI or CII substrates ..'
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:::: Introduction and Figure 1: 'A simplistic view of this convergence predicts that electron flow from N-pathway substrates sum with succinate (S-pathway) electrons to account for 100 % of the integrated ''J''<sub>O<sub>2</sub></sub> resulting from TCA cycle flux and related oxidation reactions upstream (Figure 1B).'
:::: Introduction and Figure 1: 'A simplistic view of this convergence predicts that electron flow from N-pathway substrates sum with succinate (S-pathway) electrons to account for 100 % of the integrated ''J''<sub>O<sub>2</sub></sub> resulting from TCA cycle flux and related oxidation reactions upstream (Figure 1B).'
::::::* It is difficult to interpret this sentence with its emphasis on 'TCA cycle flux and related oxidation reactions upstream'. The integrated NS-pathway flux may be controlled upstream (of Q) and downstream (of Q). If 'electron flow from N-pathway substrates sum with succinate (S-pathway) electrons' has the meaning of the two entry contributions to the integrated pathway flux, then this sentence is not a simplistic view but a definition of convergent (integrated) NS-''J''<sub>O<sub>2</sub></sub>. However, if 'electron flow from N-pathway substrates sum with succinate (S-pathway) electrons' has the meaning of the algebraic sum of the separate N-''J''<sub>O<sub>2</sub></sub> and S-''J''<sub>O<sub>2</sub></sub> (= N+S), then this view (explicit in Figure 1C) contradicts most experimental results (see Table 7.2 summarizing muscle mitochondria; Gnaiger 2020). Figure 1C should be replaced by a figure that shows the prevailing incomplete additivity. A more recent account of incomplete additivity is given in [[Komlodi 2021 BEC Q |Komlodi et al (2021)]].
::::::* It is difficult to interpret this sentence with its emphasis on 'TCA cycle flux and related oxidation reactions upstream'. The integrated NS-pathway flux may be controlled upstream (of Q) and downstream (of Q). If 'electron flow from N-pathway substrates sum with succinate (S-pathway) electrons' has the meaning of the two entry contributions to the integrated pathway flux, then this sentence is not a simplistic view but a definition of convergent (integrated) NS-''J''<sub>O<sub>2</sub></sub>. However, if 'electron flow from N-pathway substrates sum with succinate (S-pathway) electrons' has the meaning of the algebraic sum of the separate N-''J''<sub>O<sub>2</sub></sub> and S-''J''<sub>O<sub>2</sub></sub> (= N+S), then this view (explicit in Figure 1C) contradicts most experimental results (see Table 7.2 summarizing muscle mitochondria; Gnaiger 2020). Figure 1C should be replaced by a figure that shows the prevailing incomplete additivity. A more recent account of incomplete additivity is given in [[Komlodi 2021 BEC Q |Komlodi et al (2021)]].
:::: Figure 1:
::::::* There is no reference to the coupling state - is it LEAK, OXPHOS, or ET? The coupling state matters. In case of ET excess capacity, additivity in the OXPHOS state is different from the additivity in the ET state. Additivity in the LEAK state is an entirely different topic. Is the 'simplistic' view simply a view without concern of the basics of mitochondrial physiology?


:::: Introduction: 'substrate-control factors to describe the relative contributions of N- and S-pathway across a range of tissue and conditions (Gnaiger 2020).
:::: Introduction: 'substrate-control factors to describe the relative contributions of N- and S-pathway across a range of tissue and conditions (Gnaiger 2020).

Revision as of 20:50, 23 May 2022

Comments by the Editor on Introduction and Figure 1

Gnaiger E 2022-05-23
Title and Abstract: 'Multi-substrate respirometry protocols'
  • The term 'multi-substrate respirometry protocols' does not include inhibitors (rotenone) and uncouplers, both of which are important in the present respirometric protocols. For these, the term substrate-uncoupler-inhibitor-titration protocols has been introduced, which is more appropriate than 'multi-substrate respirometry protocols'.
Abstract: 'rotenone (a selective CI inhibitor) is utilized in the presence of N+S substrates to deduce the contribution of N-pathway flux to the total (N+S-pathway) JO2. .. elucidating the biological bases for variations in NS-pathway flux in multi-substrate respirometry protocols.'
  • The nomenclature in the abstract is confusing. What is the difference between "N+S-pathway JO2" and "NS-pathway flux"? - The NS-pathway is defined as the pathway with convergent electron input into the Q-junction from N- and S-substrates. N+S is the algebraic sum of the separate N- and S-pathway fluxes. The combined and summed pathway capacities are equal (NS = N+S) only in the special case of complete additivity (Gnaiger 2020, Chapters 6 and 7).
Abstract: 'under S- and some N+S pathway states, rotenone elicits a paradoxical increase in JO2, ..'
  • In the S-pathway state (without rotenone), an increase of JO2 elicited by rotenone is by no means paradoxical, but is classically expected, if oxaloacetate (inhibitor of CII) β€” accumulating in mitochondria without malate-anaplerotic capacity β€” can leak out of the mt-matrix such that its concentration is lowered after inhibiting its production by rotenone through redox-coupled NADH (product) inhibition of MDH.
Introduction: 'monitoring the effect of selective CI or CII substrates ..'
  • NADH is the substrate for CI. Monitoring its selective effect requires application of NADH autofluorescence, which is not addressed in the present manuscript.
Introduction: 'High-resolution respirometry (HRR) enables stepwise evaluation of oxygen consumption rates (JO2) in mitochondrial preparations to titrations of anaplerotic substrates that feed the TCA cycle at different sites (Gnaiger 2020).'
  • The term 'anaplerotic substrates' is too narrow to describe the stepwise evaluation of JO2. For instance, succinate is not an anaplerotic substrate when it is oxidized to fumarate and malate, and malate is - in the presence of rotenone - transported out of the mt-matrix. This has been shown most rigorously by a calorimetric enthalpy balance study in rat liver mitochondria (Gnaiger et al 2000).
Introduction: 'NAD-dependent enzymes'
  • Replace by 'NAD+-dependent enzymes'
Introduction and Figure 1: 'A simplistic view of this convergence predicts that electron flow from N-pathway substrates sum with succinate (S-pathway) electrons to account for 100 % of the integrated JO2 resulting from TCA cycle flux and related oxidation reactions upstream (Figure 1B).'
  • It is difficult to interpret this sentence with its emphasis on 'TCA cycle flux and related oxidation reactions upstream'. The integrated NS-pathway flux may be controlled upstream (of Q) and downstream (of Q). If 'electron flow from N-pathway substrates sum with succinate (S-pathway) electrons' has the meaning of the two entry contributions to the integrated pathway flux, then this sentence is not a simplistic view but a definition of convergent (integrated) NS-JO2. However, if 'electron flow from N-pathway substrates sum with succinate (S-pathway) electrons' has the meaning of the algebraic sum of the separate N-JO2 and S-JO2 (= N+S), then this view (explicit in Figure 1C) contradicts most experimental results (see Table 7.2 summarizing muscle mitochondria; Gnaiger 2020). Figure 1C should be replaced by a figure that shows the prevailing incomplete additivity. A more recent account of incomplete additivity is given in Komlodi et al (2021).
Figure 1:
  • There is no reference to the coupling state - is it LEAK, OXPHOS, or ET? The coupling state matters. In case of ET excess capacity, additivity in the OXPHOS state is different from the additivity in the ET state. Additivity in the LEAK state is an entirely different topic. Is the 'simplistic' view simply a view without concern of the basics of mitochondrial physiology?
Introduction: 'substrate-control factors to describe the relative contributions of N- and S-pathway across a range of tissue and conditions (Gnaiger 2020).
  • Substrate control factors do not provide information on the relative contributions of the N- and S-pathways to NS-JO2, except in the singular case of complete additivity. It is not clear how this statement can be derived from Gnaiger (2020).
TCA (text) and CAC (Figures 1 and 2).
  • What is the difference? Why use two different abbreviations?
Abbreviations: 'N-pathway = NADH-producing pathway'
  • It is important to distinguish a single step from the pathway. The dehydrogenase step produces NADH, the CI-catalyzed step consumes NADH. The pathway produces (in case of complete oxidation) CO2 and H2O. Respiratory N-pathway capacities are measured at (pseudo-) steady states, when O2 flux is constant over time. Under these conditions, the N-pathway keeps the redox sate of the NADH + NAD+ pool constant. As such, the N-pathway is not a NADH-producing pathway.