A KINETIC-MODEL EXPLAINING THE EFFECTS OF HYDROSTATIC-PRESSURE ON NUCLEATION AND GROWTH OF LYSOZYME CRYSTALS

The pressure-induced inhibition of lysozyme crystal growth has been examined with regard to the time scale of events in the interplay of volume changes and effects of high hydrostatic pressure. The increase in molar volume derived from high pressure experiments is confirmed by dilatometry and found to take place rapidly in comparison with the occurrence of detectable crystals. However, pressure reduces crystal yields even if it is applied in the later phase of crystallization, i.e. after nucleation and volume increase are virtually complete. This indicates that nucleation is not the only pressure-dependent process in crystallisation experiments. The overall kinetics can be interpreted in terms of the Oosawa theory of protein self-assembly, assuming a fast pressure-dependent pre-equilibrium governing nucleation and crystal growth. The equilibrium involves two conformations of the protein, one capable of being incorporated into nuclei or crystals and one that is not.