Supercritical carbon dioxide

Once upon a time, Venus may have had seas of supercritical ${\text{CO}}_2$ (${\text{scCO}}_2$) thanks to a higher surface temperature (by a few hundred Kelvin) and surface pressures (by a factor of 3 or so). However, now that the atmospheric pressure has dropped to about 9.3 MPa, this is no longer feasible aboveground; while there is plenty of ${\text{scCO}}_2$ to go around, you're unlikely to find pools of it anymore on the surface.

In subsurface oceans, however, supercritical ${\text{CO}}_2$ could still exist, and it would be a decent solvent for some enzymes. Trace amounts of water would be required, but Venus does indeed have such trace amounts in its atmosphere. Under the right conditions, ${\text{scCO}}_2$ may fit your requirements.

The enzymes

A number of enzymes react well with ${\text{scCO}}_2$, including

1. Lipases, which are involved in the hydrolysis of fats
2. Phosphatases, although these typically function optimally with water as a solvent
3. Dehydrogenases, used in certain oxidation reactions; these may involve NAD${}^{+}$ (used in glycolysis) and NADP${}^{+}$
4. Oxidases, which are used in oxidation-reduction reactions, such as part of the electron transport chain
5. Amylases, used to form sugars from starch

We need to be careful, though, as these enzymes can denature and lose their structure at many of the temperatures at which ${\text{CO}}_2$ is supercritical. Furthermore, under some conditions, ${\text{scCO}}_2$ can inhibit enzyme function, which is why it can be used for sterilization.

Experimental cases

Apparently (see the previous paper), ${\text{scCO}}_2$ has been shown to increase reaction rates in several types of bacteria; for example, it helped E. coli and Saccharomyces cerevisiae (a yeast) using $\alpha$-amylase, the most important amylase in most animals. This occurred at 20 MPa and 308 K.

posted almost 6 years ago

HDE 226868‭

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