The Use of a Magnetic Field and Magnetic Force as a Means to Improve the Quality of Protein Crystals - Molecules: Nucleation, Aggregation and Crystallization - page 211

(and dissolution) of hen egg-white lysozyme crystals (Yanagiya et al .,
2000; Yin et al ., 2001, 2002). The reason for the growth (and dissolution)
rate reduction may be complex, since it is not a simple mechanism such
as solubility change or convection suppression. Yin et al . (2001) observed
convection in a crystallizing aqueous lysozyme solution using tracer par-
ticles, but found no difference between their results with and without mag-
netic fields. An alternative reason could be a diffusion rate decrease in a
solution placed in the magnetic field due, for example, to magnetic orien-
tation of precrystalline structure or suspending microcrystals (Yin et al .,
2002; Wakayama, 2003). Whatever the reason may be, if crystals grow
slower, it is conceivable that fewer defects are introduced into the crystals.
In addition, if the advantage comes only from a slower growth rate, then
it must be ascertained whether other means (e.g. merely decreasing the
degree of supersaturation) also lead to the same quality improvement.
Studies on Crystal Perfection in Homogeneous
Magnetic Fields
Enhancement in the perfection of the crystals grown in the presence of a
homogeneous magnetic field of 10 T was demonstrated by Sato et al .
(2000, 2001). They determined rocking widths using highly collimated
synchrotron radiation on orthorhombic crystals of hen egg-white
lysozyme. It was found that the resolution limit was 1.33 Å without the
use of a magnetic field, whereas it extended to 1.13 Å when the crystals
were grown in a magnetic field. These crystals showed magnetic orienta-
tion; in this case, a thin and long crystal “stood” on a narrower plane,
instead of resting on the widest face as in the case of the absence of the
vertical field. Only the oriented crystals were used for comparison. Also,
fewer crystals grew when the magnetic field was applied. Sato et al .
(2000) suggested that the orientation of mosaic blocks in addition to the
suppression of convection were reasons for the improvement. Saijo et al .
(2005) later added the B factor and mosaicity analysis of the same crys-
tals. It is thus clear that the application of a strong magnetic field can
in fact improve the quality of a protein crystal and hence contribute to