Enzymology in perchlorate rich, multi-extreme environments
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Date
02/09/2022Author
Gault, Stewart
Metadata
Abstract
The potential for life on Mars is one of the most interesting and yet elusive
questions in modern science. The surface of Mars holds little prospect for
biology due to the large daily temperature ranges, ionizing radiation, the
presence of deleterious salts and the absence of liquid water, besides many
other contributing factors. However, deep beneath the surface of Mars we
may find environments which, while extreme in their own right, are free from
some of the more destructive factors experienced on the Martian surface.
The deep subsurface of Mars may hold liquid water environments, which
would experience high environmental pressures due to their subterranean
nature, while also experiencing extremely low temperatures, perhaps as low
as -70 °C. In order for such an aqueous environment to remain liquid at such
low temperatures, it would require the presence of saturating concentrations
of perchlorate salts which have the ability to lower the freezing of water to
temperatures around -80 °C. Such an environment provides us with three
parameters, perchlorates, pressure, and temperature, against which we can
determine the potential for proteinaceous biochemistry to exist in such an
extreme environment. How each of these individual factors affect
proteinaceous biochemistry is relatively well understood, but we know
practically nothing about how these factors interact in combination to
ultimately affect biochemistry in such a multi-extreme environment. This is
explored throughout this thesis by investigating the effects of perchlorate
salts, high pressures, and low temperatures on the activity and stability of the
model enzyme α-chymotrypsin. Additionally a meta-analysis of cold adapted
enzymes was conducted in order to facilitate a better understanding of the
fundamental adaptations which allows enzymes to become more active at
low temperatures. Through this research, I found that while perchlorate salts
lower the enzyme activity of α-chymotrypsin, high pressures can rescue this
lost activity. Furthermore, the perchlorate induced loss of enzyme activity is
found to be temperature dependent, as I have shown that perchlorate salts
can increase the activity of α-chymotrypsin at low temperatures. These
results suggest that while perchlorate rich environments are generally
deleterious towards proteinaceous biochemistry and life, the high pressures
of deep subsurface environments may counteract some of the negative
perchlorate effects, and that the perchlorate salts themselves may actually
facilitate increased biochemical potential at low environmental temperatures.
While this data does not suggest that perchlorate rich environments are
necessarily habitable or inhabited, it does provide us with a mechanistic
understanding of how biochemical adaptations could advantageously use
physical parameters such as temperature and pressure in order to increase
biomolecular perchlorate tolerance.