W0340

Phase Measurements at Cryo-Temperatures with Reference Beam Diffraction. Qun Shen, Andrew Stewart, Cornell High Energy Synchrotron Source (CHESS), Cornell Univ., Wilson Laboratory, Ithaca, NY 14853 USA.

Reference beam diffraction has been developed as an experimental method for obtaining triplet phase information from protein crystals. It is based upon the standard oscillating-crystal diffraction technique and allows a large number of triplet phases to be measured simultaneously on an area detector. Because triplet phase interference profiles may be degraded by mosaicity, so far all triplet phases measurements have been performed at room temperature using either the Renninger scan or the reference beam techniques. We report in this paper that by careful selection of triplets using the reference beam technique, it is possible to measure triplet phase interference profiles on a frozen protein crystal. This makes reference-beam diffraction one step closer to becoming a practical phasing method in crystallography.

This work is supported by NSF Grant DMR 97-13424 through CHESS and by NIH Grant GM-46733 through Hauptman-Woodward Institute in Buffalo, New York.