The catalytic activities of monomeric enzymes show complex pressure dependence

High hydrostatic pressures in the biologically relevant range (< or = 1,200 bar) are known to cause dissociation of oligomeric enzymes in vitro, whereas protein denaturation requires pressures far beyond this range. Pressure-induced inactivation phenomena attributable to neither of these effects are shown to occur in monomeric enzymes. Three different types of pressure dependence can be distinguished: (1) a linear dependence of catalytic rate constants on pressure, as predicted by the activated complex theory, observed for lysozyme and thermolysin; (2) a biphasic profile consisting of two linear contributions, found for trypsin; (3) maximum curves, as observed for both directions of the octopine dehydrogenase reaction. The third case may be ascribed to a pressure-induced decrease in the partial specific volume of the protein, resulting in reduced flexibility of the active site. This mechanism may also apply to the pressure-induced inactivation of assembly systems stabilized against dissociation in the cell.