Division of Synchrotron Radiation Instrumentation, RIKEN/SPring-8^* JASRI/SPring-8^** RIKEN/SPring-8, JASRI/SPring-8^***
○Kunio Hirata^* Nobutaka Shimizu^** Kazuya Hasegawa^** Masaki Yamamoto^***

Precisions of diffraction data crucially govern qualities of entire structural analyses of target protein molecules in protein crystallography. This is especially true for data colletion at undulator beamlines, where we often face up to difficulties in collecting good data because of 'source-specific' problems.
Generally, high flux and highly collimated X-rays available at undulator beamlines are believed to provide us 'the best quality datasets' from a view point of the fundamental crystallographic statistics compared with other radiation sources. It is true in most cases, but sometimes the source badly affects data qualities because of radiation damages and narrow rocking profiles of diffracted spots, and so on.
We conducted more than 100 diffraction data collections using several species of cryo-cooled protein crystals at the undulator beamline BL41XU at SPring-8 under various experimental conditions in order to demonstrate dominant parameters for the best data acquisition. Experimental conditions were modified by choosing several beam sizes, exposure times, oscillation widths, oscillation repetition times and pixel resolution of the CCD detector. All of the datasets were processed with several data reduction suites, such as HKL2000, MOSFLM/SCALA, XDS and DENZO/SCALA. Comparing statistical and crystallographic parameters among these datasets, key conditions governing precisions of diffraction data will be discussed.