The surface conditions on Mars present considerable challenges to habitability and the potential for biochemistry. However, deep beneath the Martian surface we find environments, such as subglacial lakes (whose numbers seem to be increasing) and deep groundwater, that are potentially more hospitable. One considerable challenge to biochemistry remains in these deep environments, and that is the predicted high concentrations of perchlorate salts which are known to be highly deleterious to life. In addition to high perchlorate concentrations, these deep aqueous environments would also be characterised by high pressures and incredibly low temperatures. This begs the question whether there is an interplay between perchlorates, pressure and temperature that would either aid or hinder biochemistry. Therefore in this study we have taken the first steps to explore the interplay between perchlorates and high pressures and how this affects enzyme activity.
This work was undertaken by myself and Charles S. Cockell of the UK Centre for Astrobiology at the University of Edinburgh, and Michel W. Jaworek and Roland Winter at TU Dortmund. We used α-chymotrypsin as an archetype for digestive enzymes and examined how its activity and stability changed with increasing magnesium perchlorate concentrations and pressure. We saw that the activity of our enzyme was diminished in the presence of perchlorates, but that the activity progressively increased with the addition of pressure. In addition to this it was shown that perchlorates shift the folded phase space of our enzyme to both lower temperatures and pressures.
These results suggest that while enzymatic biochemistry is hindered by perchlorates, the high pressures that would be felt in deep Martian environments may have the potential to overcome this loss in activity. We were also interested in the shifting protein folded phase space as it suggests that the temperature plays a vitally important role in the habitability and potential biochemistry of deep Martian environments.
The ability to interrogate how multiple parameters affect the potential for biochemistry in extreme environments represents the greatest, and most interesting challenge in our ability to understand this phenomenon. These challenges are largely technological with most apparatus designed to investigate one physical extreme or the other. As a result, the area of high pressure, sub-zero biochemistry remains largely terra incognita and as such is rife for discovery. This is in many ways the gift of astrobiology, in that it allows us to ask new and exciting questions regarding the possibility of biochemistry elsewhere in our solar system, while also answering fundamental questions about biochemistry here on Earth.