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 gro wth kinetics of the protein lysozyme. To this end, we have expanded ou r interferometry setup [Vekilov et al., J. Crystal Growth 146 (1995) 2 89] by a novel crystallization cell and solution recirculation system. This combination permits monitoring of interface morphology and kinet ics 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 prote in denaturation that is often associated with the pumping of protein s olutions. 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 increa sing u. This can be quantitatively understood in terms of the enhanced , convective solute supply to the interface. With high-purity solution s, u > 250 mu m/s lead to growth deceleration, and, at low supersatura tions sigma, to growth cessation. When solutions containing similar to 1% of other protein impurities were used, growth deceleration occurre d at any u > 0 and cessation in the low a experiments was reached al a bout half the u causing cessation with pure solution. The flow-induced changes in R-avg and nu(avg), including growth cessation: were revers ible and reproducible, independent of the direction of the u-changes a nd solution purity. Hence, we attribute the deceleration to the convec tion-enhanced supply of impurities to the interface, which at higher f low rates overpowers the effects of enhanced interfacial solute concen tration. Most importantly, we found that convective transport leads to a significant reduction in kinetics fluctuations, in agreement with o ur 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 coupl ed bulk transport-interfacial kinetics system in the mixed growth cont rol regime. (C) 1998 Elsevier Science B.V. All rights reserved.