DEVELOPMENTAL RESEARCH OF THE MEASUREMENT OF WEAK X-RAY DIFFRACTION BY USE OF AN IMAGING PLATE AND A HIGH POWER ROTATING ANODE X-RAY GENERATOR

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This research is to develop and test a method of intensity measurement of weak X-ray diffractions with the new area detector, imaging plate (IP,Fuji film Co.), and the high-power rotating anode X-ray generator 90kW in our Ultra High Intensity X-ray Diffraction Laboratory. DIP100 made by Mac Science Co.Ltd which installs an IP on the oscillation camera was combined with the above mentioned X-ray generator operated with 50kV, 50 mA on a fine focus of 0.1X1 mm. A VAX work station controls the system and processes the measured intensity data.At first we have tested a few protein crystals. (i) Tetragonal lysozyme crystal : Intensity data of a high resolution up to1.8 A^^・ could be collected in 24 hours ; 10,000 independent reflections could be collected out of a total 30,000 intensity recorded on 31 IP's, with 40 min. exposure per an IP, <I/ sigma(I)> - 5 at the limit of 1.8 A^^・ resolution, and merging R=4%. Such a speedy intensity collection with high precision are much more than expected. (ii) a crystal of a protease inhibitor protein : A complete intensity data up to 2.2 A^^・ resolution could be collected within 10 hours ; 21 IP's were used with an exposure of 25 min. per IP, merging R was 8%. The quality of this inhibitor crystal was not so good, and this limit of resolution of the data is the same as that collected at the Photon Factory of the National Laboratory for High Energy Physics. These two intensity data sets were independently used for the refinement of the protein structure and both gave the same result. (iii) alpha-amylase : Since the crystals were very small, - 0.1 mm, no high quality data set could be obtained. But it was made clear that even for small crystals this intensity measurement system could conveniently be used for testing crystal quality and heavy atom replaced crystals.Thus, this system is found to be very effective for X-ray protein crystallography.