Protein crystal growth under forced solution flow: experimental setup and general response of lysozyme

We have experimentally studied the effects of solution flow on the growth kinetics of the protein lysozyme. To this end, we have expanded our interferometry setup [Vekilov et al., J. Crystal Growth 146 (1995) 289] by a novel crystallization cell and solution recirculation system. This combination permits monitoring of interface morphology and kinetics with a depth resolution of 200 Angstrom at bulk how rates of up to 2000 mu m/s. Particular attention was paid to the prevention of protein denaturation that is often associated with the pumping of protein solutions. We found that at bulk flow rates u < 250 mu m/s the average growth rate and step velocity, R-avg and nu(avg), increase with increasing u. This can be quantitatively understood in terms of the enhanced, convective solute supply to the interface. With high-purity solutions, u > 250 mu m/s lead to growth deceleration, and, at low supersaturations sigma, to growth cessation. When solutions containing similar to 1% of other protein impurities were used, growth deceleration occurred at any u > 0 and cessation in the low a experiments was reached al about half the u causing cessation with pure solution. The flow-induced changes in R-avg and nu(avg), including growth cessation: were reversible and reproducible, independent of the direction of the u-changes and solution purity. Hence, we attribute the deceleration to the convection-enhanced supply of impurities to the interface, which at higher flow rates overpowers the effects of enhanced interfacial solute concentration. Most importantly, we found that convective transport leads to a significant reduction in kinetics fluctuations, in agreement with our earlier expectations for the lysozyme system [Vekilov et al., Phys. Rev. E 54 (1996) 6650]. This supports our hypothesis that these long-term fluctuations represent an intrinsic response feature of the coupled bulk transport-interfacial kinetics system in the mixed growth control regime. (C) 1998 Elsevier Science B.V. All rights reserved.