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Does the synthesis of water in the final step of the electron transport chain significantly increase the electrochemical gradient across the matrix? I understand that pumping protons out of the matrix clearly increases the positive charge in the intermembrane space, but the chemical reaction in Complex IV O2 + 4H+ + 4e− → 2H2O also reduces the protons in the matrix by binding them in water.

Since ATP synthase relies entirely on the electrochemical proton gradient, it seems like this might be worth mentioning, yet I haven't seen this explicitly explored in any textbooks. If there is any literature about this topic, I would love to see it.

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Your description of it is largely correct, but the electron transport chain does not simply "dump" charged oxygen ions in the mitochondrial matrix. Instead, cytochrome C oxidase (complex IV) binds the O$_2$ molecule to one of its heme groups, and the reduction O$_2$ + 4 H$^+$ + 4 e$^-$ $\rightarrow$ 2 H$_2$O occurs at the heme group before water is released. Some more details on the enzyme is found here and here (or in any biochemistry book).

In theory you're right that producing water in the mitochondrial matrix would dilute the H$^+$ concentration there a little (along with the concentration of everything else). But this dilution is negligible: the mitochondrial matrix has pH $\approx$ 7.8, which is the same as a H$^+$ concentration of about 15 x 10$^{-9}$M, while the concentration of water (yes, there is such a thing ;) is 55 M. So adding a water molecule has virtually no effect compared to removing a proton.

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  • $\begingroup$ Thanks for the explanation. Although I still have the same question - does the removal of the protons (H+) inside the matrix in the the final reduction step (O2 + 4 H + 4 e− → 2 H2O) increase the electrochemical gradient? Protons are not only being pumped out of the matrix, but they are being bound up - 2 per water molecule. Then in addition to being bound up, they're also diluted. I could've been a little more eloquent before. $\endgroup$ – Ryan Ward Jun 15 '16 at 14:54
  • $\begingroup$ Ah, I see. Yes, in this sense respiration does affect pH I think, although it is counterbalanced by H+ production in metabolic pathways. But I think the H+ concentration in the intermembrane space (cristae) is much more important for the concentration gradient, since this space is much smaller, adding a protein there has a larger effect than removing a proton in the mitochondrial matrix. $\endgroup$ – Roland Jun 15 '16 at 16:09
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The missing science to the question is the failure to realize that water inside a cell is bound to hydrophilic proteins which form an exclusion zone. This EZ is well described in the literature by Pollack. The EZ carries a strong net negative charge and it excludes protons. This has also been confirmed by numerous researchers across the world. The exclusion zone has specific physical properties that make it a different form of matter from bulk water that biologist normally are familiar with. This is why Cayetano's question is excellent and why the answer he has been given is incomplete. Any addition to the charge dramatically affects the charge across the membranes in mitochondria because they are only 4-6 microns thick. The biophysics and mathematics of cell membrane electrochemistry prove that small charge differences are magnified on membranes of this thickness. The charge across this inner mitochondrial membrane is massive. It has been shown that this change across this membrane causes a pH gradient as well as an electrical charge of about 150 millivolts across the inner mitochondrial membrane. This may sound like a small amount of charge, but consider how charge is calculated and then scaled by math: the inner membrane is only 4-5 nanometers thick, so the voltage across this membrane is about 30 million volts per meter! Dr. Nick Lane from the UK has done this work and it is published in his book called "The Vital Question" You can google his name for all the cites you want. For comparison, that is equivalent to the energy in a bolt of lightening. It is an electrical gradient that drives electrons from food to reduce oxygen from our lungs.I would also direct the readers to Dr. Martin Chaplin's work on water which takes Pollack's work to the quantum level. EZ water is a capacitor for light energies from the sun. All redox reactions in the body are tied at some level to the photoelectric effect, water chemistry, and the electromagnetic force. I will remind everyone reading this that the EMF only deals with charge particles. Electrons and protons are those particles and both are found in mitochondria in massive quantities. All foods are broken down into electrons to enter ECT.

Glutathione production in cells links the photoelectric effect in foods. When we are oxidized, we use up our stores of cysteine and glutathione. Excessive inflammation (High proton content), from any cause, does not allows cells to replenish its levels and it does not allow us to separate water into its positive and negative charges and create large exclusion zones in mitochondria. This limits energy production in a cell while slowly degrading cell signaling. We see this in % heteroplasmy increases as laid out by Dr. Doug Wallace's seminal work on mitochondria.

References:

  1. Gerald Pollack "The Fourth Phase of Water." 2013
  2. Dr. Jodi Nunnari, Professor and Chair of Molecular and Cellular Biology at the University of California, Davis was one of Wallace's post doc's: Her work in size and shape links water thermodynamics to mitochondrial energy production, see this article.
  3. Dr. Doug Wallace: Head of mitochondrial medicine at the Children Hospital of Philadelphia. - youtube.com/watch?v=KwbIR2yUziw - youtube.com/watch?v=ahlDLjf8c90

  4. Dr. Nick Lane You can google his publications which are large or just read his books "Oxygen", "Power Sex and Suicide", "The Vital Question".

  5. ER-mitochondria contacts couple mtDNA synthesis with mitochondrial division in human cells
  6. Genetics: Mitochondrial DNA in evolution and disease
  7. Scientists Learn How Mitochondrial DNA Replication is Controlled
  8. Here is Martin Chaplin website: He is a PHD researcher from the UK.
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    $\begingroup$ Welcome to BiologySE - Thanks for your contribution. As with all of the answers we appreciate citable references, such that others can follow your answer and read further. Please see the help page on "How to write a good answer" for more information - Thanks! $\endgroup$ – Vance L Albaugh Jul 20 '16 at 1:15

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