In-situ hydrolysis rate constants of ATP as a function of p-T-X, exploring the limits of life

In recent decades varies extremophiles were found deep in the lithosphere. Experimental studies showed that life is possible at 121 °C (Takai et al. 2008) and the gigapascal range (Sharma et al. 2002), which is beyond the p-T-range of the investigated lithosphere. Knowledge on the kinetic stability of vital molecular compounds, like ATP, can help us constraining the conditions possible for life.

All metabolism relies on the exergonic enzymatic hydrolysis of adenosine triphosphate (ATP) to adenosine diphosphate (ADP). At elevated temperatures, the enhanced kinetics of the non-enzymatic hydrolysis counteracts the enzymatic driven reaction; hence, it will limit the bioavailability of ATP.

We used an autoclave and a hydrothermal diamond anvil cell attached to a Raman spectrometer for in-situ investigation of the p-T-X-effects on the kinetics of the non-enzymatic ATP hydrolysis. At vapor pressure the half-lives were about 2-5 mins at 120 °C (Moeller et al. 2022). Up to 140 MPa, all results show an Arrhenian relationship in the T-range of 80-120 °C. The pressure effect can be best described by a power law; below 500 MPa the p-effect is vanishingly small, and above the rate constant increases exponentially. Addition of MgCl₂ up too 4 wt% slows down the hydrolysis. A distinguished effect of NaCl and CaCl₂ was not observed.  

The proposed limit for ATP-based life of 195 °C by Moeller et al. (2022) is lowered by additional pressure or elevated by MgCl₂, respectively. These observations strengthen the idea that life could exist far deeper in the lithosphere as discovered yet.