High pressure effects on proteins and other biomolecules.

In a discussion about pressure effects on deep-sea animals, Regnard (100) showed that pressures below 1 kbar do not irreversibly affect enzyme processes in bacteria. In contrast, pressures up to 8 kbar coagulate ovalbumin irreversibly (7). These observations have dominated the field of pressure research on biological molecules for some time: pressure effects were assumed to be reversible below I kbar and irreversible at higher pressures. More recently it was found that low pressures affect protein-ligand binding (58) and protein-protein interactions (45); the reversibility at higher pressures depends on the nature of the protein and the solvent conditions (121). On the other hand, it has been shown that DNA is pressure resistant (Il l ) and the melting temperature of lipids is strongly pressure dependent (23, 119). Since then two lines of research are discernable: the biological ap­ proach, which seeks to understand deep-sea phenomena (63, 78), and the physicochemical approach in which pressure is used as a tool to study the behavior of biological molecules. In this review we concentrate on the physicochemical approach. Activation and reaction volumes provide information on reaction mechanisms that is not available from other studies. This is illustrated in reviews on pressure effects in organic (2) and inorganic chemistry (95). Generally, the response of a system to the application of pressure is governed by the principle of Le Chatelier, which states that if a system can shrink, it will reduce its volume upon squeezing (44). This reduction in volume can be the consequence of a chemical reaction or a closer packing of the molecules. It is obvious that