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 209

disorder in the crystalline lattice than the cases where the crystals grow
mostly by the screw dislocation mechanism or by two-dimensional nucle-
ation in which crystals basically grow by attachment of one molecule to
the next molecule. If a magnetic field is applied so as to orient the direc-
tion of the merging and merged crystals, then the degree of disorder may
be reduced. This is one of the effects expected from the application of the
magnetic field. It must also be pointed out that for stronger magnetic
fields, the smaller microcrystals can be aligned overcoming thermal agi-
tation. Hence, the application of a strong magnetic field may be effective
in increasing order. A similar line was taken by McPherson (1999), who
considered that improvements in microgravity-grown protein crystals was
achieved owing to the absence of deterioration due to the sedimentation
of three-dimensional nuclei.
Other Studies on Magnetic Orientation
of Protein Crystals
The understanding of diamagnetic orientation became clearer in the
1990's due to the efforts of various groups of investigators.
Magnetic orientation was independently investigated by another
Japanese group (Sazaki et al ., 1997; Yanagiya et al ., 1999). The protein
that exhibited orientation was again hen egg-white lysozyme, and a homo-
geneous magnetic field of 10 T was provided with a superconducting
magnet. The crystal number (i.e. nucleation) and habit were also reported
to be affected by the magnetic field. It should be noted that we have not
confirmed the latter two kinds of variations in the presence of a (homo-
geneous) magnetic field as a general tendency. The other protein these
authors studied, ferritin from horse spleen, is not expected to show mag-
netic orientation, since the crystal symmetry is cubic, lacking in magnetic
anisotropy.
A French group also reported the magnetic orientation of porcine pan-
creatic amylase and bovine pancreatic tripsin inhibitor crystals in addition
to lysozyme (Astier et al ., 1998). A magnetic field of 1.25 T was provided
with a permanent magnet made of a Nd-Fe-B alloy.