An example: Carbonic anhydrase (CA) regulates the pH of the blood by converting carbon dioxide to bicarbonate. There was a model for how the enzyme does this, but pressurizing human CA II with CO2, at a pressure of 15 atmospheres, and cryocooling, let researchers actually see where the CO2 goes and confirm the model (Domsic et al. 2008, J. Biol. Chem. 45, 30766-30771). Later work allowed comparison of CO2 binding in bacterial and human CAs (Aggarwal et al. 2015, Biochemistry 54, 6631-6638).
Projects are ongoing to examine CO2 binding in other enzymes, and to extend the method to other gases such as O2, NO and NO2.
The apparatus used for pressurizing with gases such as CO2, at relatively low pressures (10-20 bar), is shown here (sketch on the left, photo on the right). Post-doc TK Chua has been instrumental in developing this apparatus and applying it to answer biological questions.