Highly Purified Glucose Isomerase Crystals under Microgravity Conditions Grow as Fast as Those on the Ground Do

Suppression of convection flows (solute transportation) and suppression of impurity incorporation into crystals seem to be the main reasons why the quality of protein crystals improves under microgravity, although their precise mechanisms have not been completely discovered yet. In this study, we focused on the first reason, effects of suppression of convection flows. We tried to clarify the effects on crystallization processes by in situ observation of straight steps on parallelogram-shaped spiral growth hillocks on the {110} faces of highly purified glucose isomerase (GI) crystals under microgravity conditions and on the ground. Lateral growth rates V lateral of a spiral hillock on the {110} face of a GI crystal in situ under microgravity and step velocities V step of the same configuration on the ground had similar maximum values. This similarity indicates that the convection flow has a small, if any, influence on the growth rates of protein crystals, contrary to conventional expectations. From V step of the straight step in a particular direction, we estimated the vibrational frequency of a GI tetramer at a kink site of a step as 229.8–1182 s–1 with the assumption of zero activation energy of kink incorporation processes.