Crystals of porcine pancreatic elastase can be derived by soaking in
high-molarity bromide solutions. These crystals, either in a glycerol-based
cryoprotectant solution or in paraffin oil, can be subsequently pressurized
under a xenon atmosphere to incorporate xenon. When paraffin oil is used, a
larger number of bromide ions are observed on the protein surface. Intensity
data collected to lower energy than the bromine absorption edge can be used to
determine the xenon position and the resultant phase information can be used to
determine the bromine substructure from data collected to higher energy than the
bromine absorption edge. The method would appear to have general applicability
where large substructures need to be determined.
Figure 1.
Figure 1 The Harker sections of the anomalous difference
Patterson for (a) the Br-Xe-G1-W0.93 and (b) the Br-Xe-G1-W0.8
data set. The expected vector positions are marked with circles
and the xenon (261) and bromide vectors are numbered as in Table
2-.
The above figure is
reprinted
by permission from the IUCr:
Acta Crystallogr D Biol Crystallogr
(2002,
58,
1413-1420)
copyright 2002.
