Pressure dependence of subtilisin crystallization kinetics

The effect of pressures from atmospheric to 100 MPa on crystallization of P urafect subtilisin was investigated. The overall crystallization rate was l ower at high pressures and short exposures to high pressure followed by atm ospheric crystallization did not increase the overall crystallization rate. Subtilisin solubility increased with pressure from 1.1 mg/ml at 0.1 MPa (a tmospheric pressure) to 2.9 mg/ml at 68 MPa giving a calculated volume chan ge for crystallization as 30 +/- 7 cm(3)/mol. Linear crystal growth rate dr opped with increasing pressure in the range 0.1-13.6 MPa. The dependence of growth rate on supersaturation at 0.1 MPa changed from an exponent of 0.18 at high supersaturation to 2.8 at lower supersaturation indicating a possi ble change in the rate limiting step. At high pressures, single values of t he exponent sufficed but the value increased to 4.2 at 6.8 MPa and 6.3 at 1 3.6 MPa. Crystal size distributions (CSD) were obtained after crystallizati on with agitation. Pressure decreased the crystallization rate in these exp eriments also. Nucleation rate expressions were obtained by simultaneously fitting a population balance model to the residual soluble protein concentr ation and final crystal size distribution data. (C) 2000 Elsevier Science B .V. All rights reserved.