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 206

Prior to the experiments described above, Rothgeb and Oldfield
(1981) had used myoglobin (from sperm whale) crystals to study the
effects of a static magnetic field of 0.3 T. In this case, already-grown and
sedimented crystals were vigorously agitated to detach them from the ves-
sel and then the vessel was placed in the magnetic field. With such exper-
imental procedures, the suspended myoglobin crystals are considered to
have sedimented to the vessel bottom in the presence of the magnetic field
(the crystals do not grow in this case). Considerable orientation was
observed, which was absent if the field was not present. The magnetic ori-
entation was ascribed to the Fe ion contained in the heme in the myoglo-
bin molecule, more specifically, to the anisotropy of the paramagnetism.
Therefore, it was not clear from these analyses whether most proteins that
do not contain Fe ions magnetically orient or not. Note also that the func-
tion of myoglobin in mammals including whales is to store oxygen in
muscle and other parts of the body.
Our Studies on Magnetic Orientation
One of the main messages intended to be delivered in this chapter is the
idea that magnetic orientation may in principle be used (at least in favor-
able cases) to reduce misalignment in protein crystals and to obtain better
quality crystals. Microgravity in space has sometimes been suggested as a
potential environment that can be used for similar purposes; however, the
use of magnetic orientation may also be considered on some occasions.
Protein crystals grown in a magnetic field
exhibit orientation
As shown in the section on “Historical Background” (p. 8), tetragonal
lysozyme crystals exhibit orientation coming from diamagnetic anisotropy.
We first used this fact to know when the crystals sediment to the bottom of
the vessel (Ataka et al ., 1997). Usually, when we observe the crystals grown
from a supersaturated solution of 1 ml or more using an optical microscope,
nearly all of them are found to be at the bottom of the glass vessel. If the