A compact x-ray system for macromolecular crystallography

We describe the design and performance of a high flux x-ray system for a ma cromolecular crystallography that combines a microfocus x-ray generator (40 mu m full width at half maximum spot size at a power level of 46.5 W) and a collimating polycapillary optic. The Cu K alpha x-ray flux produced by th is optimized system through a 500 mu m diam orifice is 7.0 times greater th an the x-ray flux previously reported by Gubarev [M. Gubarev , J. Appl. Cry stallogr. 33, 882 (2000)]. The x-ray flux from the microfocus system is als o 2.6 times higher than that produced by a rotating anode generator equippe d with a graded multilayer monochromator (green optic, Osmic, Inc. CMF24-48 -Cu6) and 40% less than that produced by a rotating anode generator with th e newest design of graded multilayer monochromator (blue optic, Osmic, Inc. CMF12-38-Cu6). Both rotating anode generators operate at a power level of 5000 W, dissipating more than 100 times the power of our microfocus x-ray s ystem. Diffraction data collected from small test crystals are of high qual ity. For example, 42 540 reflections collected at ambient temperature from a lysozyme crystal yielded R-sym=5.0% for data extending to 1.70 Angstrom, and 4.8% for the complete set of data to 1.85 Angstrom. The amplitudes of t he observed reflections were used to calculate difference electron density maps that revealed positions of structurally important ions and water molec ules in the crystal of lysozyme using the phases calculated from the protei n model. (C) 2000 American Institute of Physics. [S0034- 6748(00)01211-9].