Saturday, 16 January 2010

Enzymes

I have started to discuss my theory with Gary Taubes and this blog post is intended to go into a bit more detail about how stuff works. Trying to explain the following over the phone with hand-waving is likely to be very difficult, especially when I forget things!

Firstly, see Enzyme. Their name always ends in "ase". The thing about enzymes is that their activity can be increased & decreased by the level of substrate i.e. how much "stuff" there is going in to the reaction and how much "stuff" there is coming out of the reaction. Activation & inhibition can also be produced by other substances not directly involved in the reaction.

To get from Glucose (assuming muscle cells) to Pyruvate involves a multi-step process involving lots of different enzymes and other substances. Here's the first step.

Glucose + 1 molecule of ATP (Adenosine Tri-Phosphate) is converted by Glucokinase (with the aid of 2 Magnesium ions) into Glucose-6-phosphate + 1 molecule of ADP (Adenosine Di-Phosphate) + 1 Hydrogen ion. Here's the last step.

Phosphoenolpyruvate + 1 molecule of ADP is converted by Pyruvate kinase (with the aid of 2 Magnesium ions and 1 Potassium ion) into 1 molecule of Pyruvate + 1 molecule of ATP.

As stated in Everyone is Different , muscle cells at rest derive most of their energy from fat (Tri-Palmitin). Inside the cell mitochondria, molecules of Palmitoyl CoA (from Palmitate from hydrolysed Tri-Palmitin) produce energy starting with a process called beta-oxidation, where Acetyl CoA is repeatedly "snipped-off" yielding a fatty acid that's shorter by 2 carbon groups, 1 molecule of Acetyl CoA, 1 molecule of FADH2 + 1 molecule of NADH+H+ (don't ask!) until all that's left is Acetyl CoA. The molecules of Acetyl CoA enter the Krebs Cycle which produces more energy.

As muscle cells at rest derive most of their energy from Acetyl CoA rather than Pyruvate, Pyruvate accumulates. This inhibits the enzyme Pyruvate kinase causing an accumulation of Phosphoenolpyruvate. This inhibits the enzyme that produces Phosphoenolpyruvate etc etc. This results in an accumulation of Glucose-6-phosphate. This inhibits the enzyme Glucokinase causing an accumulation of Glucose. This inhibits the Glu-T4 transporters making muscle cells temporarily insulin resistant. Blood glucose stops entering muscle cells.

Things change when muscle cells undergoing anaerobic exercise use Pyruvate instead of Acetyl CoA. A lack of Pyruvate activates the enzyme Pyruvate kinase causing a lack of Phosphoenolpyruvate. This activates the enzyme that produces Phosphoenolpyruvate etc etc. This results in a lack of Glucose-6-phosphate. This activates the enzyme Glucokinase causing an lack of Glucose. This activates the Glu-T4 transporters making muscle cells temporarily insulin sensitive. Blood glucose enters muscle cells even if blood insulin level is normal.

The same principle applies to fat cells regarding glycerol-3-phosphate. In conclusion:
Within cells, the biochemical processes that produce "stuff" are not static but vary according to the needs of the cells.

I need a break!

While waiting to get hold of Taube's book Good Calories Bad Calories, I'm reading Toban Wiebe's Complete Notes to Good Calories, Bad Calories by Gary Taubes.

I'm also reading Anthony Colpo's latest articles on http://www.anthonycolpo.com/ . This guy doesn't mince his words!

6 comments:

LynMarie Daye said...

Hi Nige,

I get what you're saying here and think it's a well thought out theory. I can see a potential point of contention however. Getting glucose inside a fat cell is the first major step in the production of G3P. The second major phase is getting the glucose to go through glycolysis, and an argument can be made that glycolysis doesn't happen much when a lot of fatty acids are being "burned" for energy. As you know I'm sure, during LCHF dieting our bodies switch to a fat-burning mode. I need to refresh my memory regarding how glycolysis and beta-oxidation relate to one another, but I think some product of fatty acid oxidation builds up and inhibits glycolysis. Time to break out the Biochemistry text yet again!

Nigel Kinbrum BSc(Hons)Eng said...

Hi LynMarie,

Normally, when a cell burns FAs, the Acetyl CoA produced stops pyruvate from entering Krebs and the accumulation of pyruvate down-regulates glycolysis.

However, taking in lots of FAs depletes glycerol-3-phosphate which up-regulates glycolysis, or to be more specific, the pentose phosphate pathway.

Nige.

LynMarie Daye said...

Thanks Nige, that makes sense and rings a few memory bells. :`P

Did I read your post correctly and you're going to be discussing this with Gary Taubes over the phone?

Nigel Kinbrum BSc(Hons)Eng said...

That was the original plan. However, when I admitted that I hadn't read GCBC, Gary advised me to read it before disagreeing with any of it.

Having read the notes to GCBC, I don't think that there's much point in me buying the book for the sake of the 1% of it that I disagree with. I therefore don't think that there's going to be a phone discussion now.

I much prefer to have discussion here for all to see. It also gives me time to look stuff up!

Dr.A said...

Nige, how about discussing your theory with James Carlson? He did biochemistry.

Nigel Kinbrum BSc(Hons)Eng said...

I have left a comment on Back to That Calorie Thing.....?