Using Enzymes to Help Fight CO2 Build-Up

A reader writes to us: "There is a story in the New Scientist that details efforts to use enzymes that destroy ethanol as catalytic converters, turning noxious carbon dioxide into methanol. " The enzymes in question are actually those that are found in the liver - the same one that helps break down alcohol. Cool application of it, if this ever becomes reality.

Comments

Hmmm...

[jd]

CO2 is far from being the worst of the greenhouse gasses, and it's already being converted quite nicely into O2 by trees and plants. (Mind you, humans seem to have a habit of turning said trees and plants into lots more CO2 by burning them, to make way for McDonald ranches, in the area formally known as the Rainforest.)

By far the nastiest gasses are NO2 and SO2. These give you that icky brown and yellow smog, which you can see over many industrial cities and major roads during a temperature inversion. They are also the predominant gasses on Venus and are the primary cause of the hellhole nature of that world. They also contribute FAR more to the greenhouse effect than carbon dioxide.

Now, if the enzymes could do something useful with those, I'd be impressed. Clean up smog AND remove the greenhouse effect in one easy sweep. Anyone want to develop a sulpher-based life-form?

Re:New Scientist is sloppy: chemistry misses steps

[aswang]

Here's a theoretical pathway (the real mechanism will certainly be a lot messier, involving enzyme-substrate intermediates):

CO2 + H20 <==> H2CO3
(occurs without catalysis, but can be sped up by carbonic anhydrase)
H2CO3 + NADH + H+ <==> HCOOH + NAD+ + H2O
(catalyzed by formate dehydrogenase)
HCOOH + NADH + H+ <==> HCHO + NAD+ + H2O
(catalyzed by formaldehyde dehydrogenase)
HCHO + NADH + H+ <==> CH3OH + NAD+
(catalyzed by alcohol dehydrogenase)

Net reaction: CO2 + 3NADH + 3H+ <==> CH3OH + 3NAD+ + H2O

I think that's balanced. Biochemists are often lax about mentioning hydrogen ions and water molecules in a reaction because it's generally assumed that they're present in abundance in biological conditions.

This is a joke, right?

[fnj]

This is a joke, right? I mean, no one could be so stupid as to think that changing massive quantities of comparatively harmless CO2 into highly toxic methanol is desirable on a large scale.

Methanol is not ethanol. Methanol is toxic when drunk, toxic when the vapor is breathed, toxic when absorbed through the intact skin, and really bad news if you squirt a couple of drops in your eye.

Besides, methanol's only uses are as a fuel and as a raw material for making other compounds. When you burn or catalyze the Methanol as fuel, you get the CO2 back again, and when those other compounds are eventually consumed or destroyed, you get the CO2 back again (and other noxious compounds, by the way).

CO2, on the other hand, is food for plants. If you "cleaned" the atmosphere entirely of CO2, all plants would die, no more O2 would be produced, and eventually all O2 would be consumed and all animals would die. Yes, we are animals, and we would die too.

The New Scientist article is baffling because it seems to have things backwards. Our livers (in the unhappy event anyone is foolish enough to consume methanol - not ethanol) in fact convert methanol into formaldehyde and formic acid, not the other way round. It is this formaldehyde and formic acid that account for the toxic effects - notably permanent blindness and destruction of the nervous system and cerebral cortex (not real fun). I know the article waves its hands and says, oh, the process is reversible. Maybe...