Hi everybody!
I have made the following funny observation with crystals of a 24 kDa
protein: the spacegroup of the crystals is P42(1)2, but under the
polarizing microscope they show birefringence along the 4-fold axis,
exhibiting a checked pattern like this:
|XXXXXXXXXXXXXXX|
| XXXXXXXXXXX |
| XXXXXXX |
| XXX |
| X |
| XXX |
| XXXXXXX |
| XXXXXXXXXXX |
|XXXXXXXXXXXXXXX|
Can anyone give me an explanation for that? I'm quite sure that the
spacegroup is correct since I could solve and refine the structure to
an r-factor of well below 20% at 2.1 A resolution. Furthermore, after
statistical analysis of the observed intensities I'm sure not to have
twinning in my crystals, which could give rise to a higher apparent
symmetry.
Thanks for any comments!
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Matthias Dreyer
Institut fuer Org. Chemie und Biochemie
Albertstr. 21
D - 79104 Freiburg
Germany
e-mail: dreyer at bio5.chemie.uni-freiburg.de
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