Monday, August 19, 2019

Protons (49) Complex III

Dave Speijer, an extremely insightful person if ever there was one, has a new paper out:

Can All Major ROS Forming Sites of the Respiratory Chain Be Activated By High FADH2/NADH Ratios?

the link to which I am extremely grateful to Bob for forwarding to me. This concept is purely from Dr Speijer. But I like it. A lot.

I'll start with an old doodle I produced about a decade ago depicting the front end of the electron transport chain. Matrix is at the top, cytoplasm at the bottom:

Electrons travel from NADH to Coenzyme Q, reducing it to QH2 which donates them to complex III being oxidised back to Q in the process.

The unlabelled blobs in the diagram are complex II (succinate dehydrogenase), electron transporting flavoprotein dehydrogenase and mitochondrial glycerophosphate dehydrogenase, all of which compete with complex I for CoQ as an electron acceptor. Given a high membrane voltage, a deeply reduced CoQ couple with most of the CoQ as QH2, then reverse electron transport back through complex I gives superoxide/H2O2 generation (provided the mitochondrial NAD pool is also highly reduced so unable to accept electrons (ie little NAD+, lots of NADH).

This is pretty straight forward and is the gist of the Protons thread. The extension of this is that, under high substrate availability, H2O2 from this process stops insulin facilitated caloric ingress to the cell.

Another major site of ROS generation in the ETC is complex III. Dave Speijer would hold that this is also triggered, like RET, by a deeply reduced CoQ couple. This is why.

So here is a stripped out version of the above doodle:

The problem here is that it's not that simple. Complex III does rather odd things with its two electrons. Electron bifurcation is a standard enzymic technique perfected very early on by proto-biology and it is exactly what happens here. One electron travels to cytochrome C (which only ever carries one electron at a time) and then on to complex IV and O2. The other does not:

The second electron is transferred backwards to another  CoQ molecule and so partially reduces it to QH*, the radical semiquinone.

So (oxidised) Q is a necessary electron acceptor for complex III. Under high substrate availability and with most of the CoQ couple present as QH2 there will be very little Q available.

With one electron securely on cytochrome C, with any delay in the availability of Q, the second electron can be left sitting on one of the two haem groups along its route, easily available for donation to O2 to give superoxide, so adding its ROS signal to that of complex I. Both indicate that enough substrate is present and it is time to limit insulin signalling, to limit caloric ingress.

Nothing, absolutely nothing, about the construction of the ETC is random.

The general principle that a highly reduced CoQ couple is a signal to halt caloric ingress in to the cell applies to complex III just as much as to complex I.

When you want to resist insulin, you really want to resist insulin. Superoxide is then your friend.

If you fail to limit caloric ingress then eventually ROS from complex III are ideally placed to break the cardiolipins which anchor the water soluble cytochrome C to the inner mitochondrial membrane. Destroy these anchors and the ROS signal changes from"resist insulin" (good) to "perform apoptosis" (possibly not quite so good)...

And of course ROS in excess of physiological signalling are going to activate all sorts of inflammatory pathways.


Aside: The process of ROS generation is probably limited by pairing of complex IIIs (complex III is always a dimer in-vivo) for cooperation to use one Q to accept an electron from each of the pair. This should limit ROS generation as one Q will be available to two complex IIIs, twice that avaiable if they were each working alone. Nothing is random. End aside.


Ken Strain said...

Wonderful! By chance reading Speijer's 2016 Q evolution paper today, a good warm up for this one. Follow the electrons - step by step along the ETC.

Peter said...

Glad it's timely. Speijer has some excellent ideas!


Bob said...

Please help me understand something. At first the Protons thread suggested ROS-driven insulin resistance focused on carbohydrate. Then we learned that insulin up-regulates CD36 receptors for fatty acid uptake.

So does physiological insulin resistance include fat as well as carbohydrate? Wouldn't surprise me it gets more complicated with each new finding.

Peter said...

Hi Bob,

The longer I look at insulin the more the phrase caloric ingress control comes to over ride the glucose ingress aspects. If you simply don’t feed a group of healthy young men for 3 days they will have a free fatty acid concentration of 2000micromol. That’s just the average. This strikes me as an essentially unlimited supply of energy to a given cell. It has to be regulated.

I’ve spent a lot of time looking at the ETC as the site of regulation of FFA oxidation and both acyl-CoA and acyl-carnitine may act at or close to CoQ binding pockets to regulate electron transport but it’s not exactly a hotbed of research. The concept of insulin resistance induced by FFAs being a regulator of FFA uptake when FFAs are high makes sense. It’s a layer up from the ETC, which is much more interesting to me but we have to accept that layers of control are what a few billion years of selection pressure comes up with!

I picked up a 2017 review

From fat to FAT (CD36/SR-B2): Understanding the regulation of cellular fatty acid uptake

which cites a massive review from 2010

Membrane Fatty Acid Transporters as Regulators of Lipid Metabolism: Implications for Metabolic Disease

which is too big to promptly follow to the next level of (old!) references which might be the basic science. Back in 2010 it was controversial how much FFA uptake was CD36 mediated and how much FABP mediated and how much was transmembrane insertion/release down a concentration gradient. It wasn’t even clear what order of magnitude FFAs were present at in the aqueous areas of the mitochondria.

Unfortunately modern research doesn’t seem driven to answer these basic question, or, if it is, the 2017 review isn’t saying!


Bob said...


Thanks for your thoughts. Perhaps as more people go "keto" and as they present to the medical profession (with mostly slimmer bodies and interesting lipids) there will be more attention paid to this research.

Peter said...

Bob, I also meant to mention that the fore-arm perfusion studies show that as you increase insulin perfusing the arm you initially inhibit lipolysis, then you translocate K+, then eventually you facilitate glucose uptake. How might CD36 translocation fit in to this type of hierarch? Dunno is the answer!

And a final thought was that in-intact insulin resistant humans glucose is elevated, but so to are FFAs and lipoproteins.


Pernickety said...

Peter, by intact insulin resistant humans, are you referencing to those with physiological (for example, when eating a very low carbohydrate, high saturated fat diet) or pathological insulin resistance? If it's the former, would you always expect glucose to become slightly elevated? Would this elevated glucose only be seen after an overnight fast or 24/7?
I ask because I know you have previously mentioned you experience elevated fasting glucose most likely due to physiological insulin resistance, and many others have reported this to be the case for them also. But not everyone eating a LCHF diet develops this, and I'm wondering if that's possibly because of ongoing lipolysis of PUFAs like linoleic acid that have been sequestered in adipose tissue over the years, which leads to increases adipose insulin sensitivity? If this is the case, once weight stable or when enough time has passed for significant adipocyte turnover to have occurred, would you expect fasting glucose to rise and any hypoglycaemic episodes to disappear?
What are the other explanations for failure to generate physiological insulin resistance (and thus experiencing occasional symptomatic hypoglycaemia) when eating a LCHF diet with an emphasis on SAT fat (including dairy) and low in PUFA? Can the adaption process take longer than a year and is there any way to speed it up? I love eating this way and feel the evidence is pointing towards a LCMPHsatF diet being most sensible long-term if you wish to minimise your risk of a variety of common modern chronic ailments, as I do, but it'd be great if I could work out a way to feel more energised and physically capable of more intense and/or regular exercise. I'd appreciate any suggestions!

Bob said...

Peter, I recall the starting point for insulin signalling was tyrosine phosphatase. The 2010 paper you cited (and, yes, that's one hell of a big meal) notes the analogies (homologies?) between glucose and FA uptake at the cellular level. How ironic would it be if the same enzyme kicked off FA signalling?

Bob said...

I suppose I should have said the crippling of tyrosine phosphatase...

karl said...

What is strange about that paper -
From fat to FAT (CD36/SR-B2): Understanding the regulation of cellular fatty acid uptake

Is that it fails to mention HSL or LPL or even the word lipase
For those interested see:

Both of these appear to be under the control of insulin.
Membrane Fatty Acid Transporters as Regulators of Lipid Metabolism: Implications for Metabolic Disease does mention HSL -- Seems like a disconnect from the complete picture? I mean there a consequence in the levels of FFA?

I don't know how wide spread consumption is in Russia and the Ukraine - but it looks like it is increasing:

I wonder what level consumption is at and when it started? Will the very fit young women there become a thing of the past?

My hunch is that at least one leg of the T2D/obesity pandemic is due to the consumption of large amounts of refined veg-oil. I wonder if there is a genetic component - some people do not seem to be so effected - PUFA - particularly LA is in a huge amount of the foods consumed today - just not human food.

The lack of research - I am told that big Ag has great influence on research grants that have to do with Veg-oils. The size of the industry is staggering - "global edible oil and fats market size was valued at USD 97.32 billion in 2018"
"money doesn't talk - it swears"(Dillon)

They have 'handlers' that watch for grants that might threaten the industry.

I particularly hate the term "insulin resistance" - it makes it sound like a 'bad-thing'(tm) - but it isn't. Compare with "lowered insulin sensitivity" or better yet normal morning insulin sensitivity.

Insulin sensitivity is not the same for all tissues - and will lead to false conclusions if you go down that road. Absolute insulin levels are not as important as changes in insulin sensitivity. There is a widely parroted false narrative that insulin is what regulates blood glucose -

One last bit - imagine some substance that causes over storage of fat - to the point where the person feels tired and hungry - very hungry. I've talked to people in the 150Kg[330lb] weight range - they tell me they are just constantly hungry. I feel for them. The problem is if protons explains the sensitivity of HPL and LPL - and the PUFAs bioconcentrate (I have a hunch - but not any good research that I've found) - if someone does calorie restriction - the fatty acids coming out of the fat tissue have historically elevated LA -

How likely are they to lose weight? I've seen the number of a 600day half life for LA.

This is the biggest health issue of our time - and the PUFA connection is not being talked about. When I mention the effect of PUFA's on weight - I am treated as a kook - no one bothers to check it out and read the papers.