W0166

Impure Thoughts in Space (Dimer Impurities in Microgravity Grown Lysozyme). Edward H. Snell, Russell A. Judge, Elizabeth L. Forsythe, Marc L. Pusey, Michael Sportiello, Paul Todd, Henry Bellamy, Jeff Lovelace, John M. Cassanto & Gloria E. O. Borgstahl, NASA Lab. for Structural Biology, Code SD 48, NASA MSFC, Huntsville, AL 35812.

Chicken egg-white lysozyme (CEWL) crystals were grown in microgravity and on the ground in the presence of various amounts of a naturally occurring lysozyme dimer impurity. No significant favorable differences in impurity incorporation between microgravity and ground crystal samples were observed. At low impurity concentration the microgravity crystals preferentially incorporated the dimer. The presence of the dimer in the crystallization solutions in microgravity reduced crystal size, increased mosaicity and reduced the signal to noise ratio of the X-ray data. Microgravity samples proved more sensitive to impurity. Crystal quality was evaluated, in part, by measurement of the angular width of hundreds of indexed reflections from each crystal. From this data we were able to calculate the anisotropic mosaicity of each. The largest crystals with the best X-ray diffraction properties were grown from pure solution in microgravity. Microgravity should not be seen as a step to replace good biochemical practice but may be useful in situations where solution impurities are formed during the crystallization process. Partitioning of impurities seems to be a complex phenomenon.