Zombie Metabolism: Citric Acid Cycle

Sorry to have been quiet for so long, I'm sure you must have thought that I had been eaten, or perhaps that I had taken eating (others) as a full-time occupation.

Well, you'll be glad to know that I am alive and well... ish. I am also completely alone. My group has abandoned me, they think I'm obsessed with zombie metabolism and that I have completely lost the plot. Well, I'll show them! Ah-hah-hah-haha-HA!

I don't need them! I broke into the biochem labs at Imperial all by myself, and guess what? Their back-up generators have been running this whole time! Partly reliant on solar power - yay for green enthusiasts, though they are sort of brownish-green by now...

Anyway... all the lab zombies were in pretty bad shape, probably the lack of vitamin D, so it wasn't too hard to get myself up and running in one of the labs.

I used to have so much respect for those professor-types, I used to be a PhD student, but it sort of takes the shine off when they dribble from their eyes... They just don't seem to have that same, I dunno, air of authority. Much more an air of rubbish. Eau de crap, if you will.

I digress.

I caught one of the lab zombies, and measured its RER (respiratory quotient, that is, the ratio of oxygen used, vs carbon dioxide produced), and that zombie was respiring veeeeerrrrrryyyyyy sssssllllloooowwwwllllyyyyy. The O2/CO2 was about 0.9, which implies that it is probably using a mixture of carbs and fat, and probably protein too. Would this be different if it had just eaten? There are limits to what I will do in the name of science, so unless I go on a serious revenge kick, I guess we'll never know...

So, what does this have to do with the citric acid cycle? Well, in previous posts, I was debating the importance to zombies of glycolysis (anaerobic) vs fatty acid oxidation (aerobic). Now that I have confirmed that they do use a fair amount of oxygen, it seems highly likely that they will be carrying out citric acid cycle reactions.

For those biochem enthusiasts out there who, despite the daily struggle for survival, despite the lack of edible food, and the numerous walking dead that lie in wait around every corner, never sleeping, never tiring, never feeling satiated in their desire for human flesh, still find a few moments to revise basic biochemistry (metabolism is life!), it is easy to remember why the citric acid cycle is so important.

But for those who have been distracted by the zombiepocalypse, a refresher:

The citric acid cycle takes in acetyl CoA, and via addition of oxaloacetate, oxidises it gradually to carbon dioxide, in a series of reactions that produce, in a roundabout way, energy for the cell. In order to make use of this energy (most of it anyway), the products of the citric acid cycle need to feed into the electron transport chain, which relies on oxygen.

I intend to do more studies on the zombie tissue, in particular the muscle and the nervous system. So guess what is so exciting about zombie research? The tissues continue to work after they have been removed from the body!!!

How cool is that? No more cell cultures for me. (I'm dancing around the lab right now.)

And they thought I was crazy...

Cheapskates!

When metabolic cycles go out to dinner...

Succs to be me...

Dear Miss Metabolism,

I am a complex II, and I am being bullied. I work just as hard as any other enzyme complex, I contribute as much as I can, but the other complexes make fun of me because I can't pump protons like they do. Even Complex V teases me, and she lets protons back in!!!

How is that fair?

I can't control the redox potential of succinate or ubiquinone, any more than they can control the redox potentials of their substrates and products.

I wouldn't mind so much, but they're making my little FAD depressed. Sometimes I hear him crying himself to sleep at night. Its not right for a little prosthetic group to hear his enzyme being humilated like this, its bad for his self-esteem.

I've tried explaining these things to the other complexes, but they just won't listen!

Any advice on how to handle this?

Yours truly,
Succs To Be Me


Dear Succs To Be Me,

The first thing I want you to do is stop talking about yourself like that! You are an important complex, and don't ever forget it!

Its true that via Complex I, the electron transport chain can continue along without you, but there is more to a half-life than transporting electrons. Its true that you don't pump protons, but there is more to a half-life than generating electrochemical gradients.

Perhaps this sounds cliche, but I am pretty sure they are just jealous. Lets not forget that the succinate dehydrogenase part of you is absolutely integral to the citric acid cycle, and what would happen if you stopped functioning? I'd like to see them get much in the way of reducing power then, the supply would become pretty scarce, I can tell you!

And in addition to all that, you might have a role in oxygen sensing and tumour suppression too!

I wouldn't be surprised if Complex I was the one instigating all this, after all, you are the competition, and he probably sees you as a threat. As for Complex III and IV, they should be ashamed of themselves, how can they make fun of you while still accepting your electrons? They would do well to remember that the real reason they can pump protons is because of the difference in the reduction potentials of their substrates and products, and not because of any intrinsic property that they have.

And my sympathies to your little FAD, although we coddle and fuss over them, don't worry, prosthetic groups are alot tougher than we give them credit for, he'll be alright, as long as you don't take their insults to heart.

Having hopefully activated your self-esteem a little bit, let me just say this. Bullies are insecure, and they crave a response from those they bully. To paraphrase a human saying, 'Enzymes need substrates'. Show them just how much you don't care, and if they really get on your nerves, take a break for a while... when the citric acid cycle grinds to a halt, they'll be begging you to start transporting electrons again.

Keep your chin up,
Miss Metabolism

Check Yourself Before You...

Wreck Yourself!

(still under development...it works, just needs a few features)