Pressure effects on activity and selectivity of Candida rugosa lipase in organic solvents

Even though a lot of high pressure studies on enzyme structure, stability and activity are published in the last years, just a few works deal with the influence of pressure on the enantioselectivity of an enzymatic reaction. Furthermore, a change of the reaction medium from buffer to organic solvents for high pressure studies offers some interesting advantages, like pH independency and higher sensitivity towards hydration changes. From this point of view, in the present paper the influence of high pressure on the activity and selectivity of a Candida rugosa Lipase catalyzed reaction in organic solvents was examined. The transesterification of 1-phenylpropan-2-ol with vinyl acetate was chosen as a model reaction. The reactions carried out at 50 MPa showed an increased specific activity of the lipase, independent of solvent composition, reaction temperature and water content of the solvent. An activity maximum, without deactivation, was observed in hexane at 45 C and 200 MPa. Between 50 MPa and 200 MPa a linear increase in the enantiomeric excess (ee_R) could be detected, also independent of the solvent composition, reaction temperature and water content of the reaction medium. Furthermore, if additional water was added to the reaction solvent no change of the ee_R at high pressures could be observed. This leads to the conclusion that the ee_R under pressure is probably mainly influenced by the compression state of the enzyme or by structural changes of the active center rather than by the water content of the enzyme, as it is the case at ambient pressure.