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

Suppression of convection flows (solute transportation) and 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. We tried to clarify effects of suppression of convection flows 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 Vlateral of a spiral hillock on the {110} face of a glucose isomerase crystal in situ under microgravity and step velocities Vstep of the same configuration on the ground had similar maximum values. This similarity indicates the convection flow has a small, if any, influence on the growth rates of protein crystals, contrary to conventional expectations. From Vstep of the straight step in a particular direction, we calculated the vibrational frequency of a GI tetramer at a kink site of a step as (1182±3) s^(-1) with the assumption of zero activation energy of kink incorporation processes.