Protein crystallization is one of the dominant experimental fields in the space utilization. A lot of space experiments have been developed since 1983. It is used to be said that at least 20％of those experiments show the positive eｆfects of microgravity on protein crystallization. Although there are many prospects for the space crystallization technology, there may be some negative reputation of current experimental status. Here I discuss about the potential of crystallization in　space based on the recent investigations. If the protein crystallization experiment in space is improved not only technically but also systemically, it will provide good opportunities to perform the crystallization of various kinds of proteins and will certainly become complementary technology of the ground based high-throughput protein structure analysis.

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Characterization parameter for protein crystals has been discussed. I/CJ is not a proper parameter. The apparent B- factor obtained by the Wilson Plot is a good parameter for the characterization of protein crystals, and the modified Wilson Plot has been proposed for obtaining B-factors. This method has been applied to the characterization of oligomer DNA and Hen Egg-White Lysozyme crystals. The intrinsic nature of the good protein crystal has been explained not by the mosaic block model but by the degree of the molecular orientation in a unit cell.

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NASDA had an opportunity to participated in ODISSEA Mission by using GCB (Granada Crystallization Box last year. We conducted the crystallization experiment using alpha-amylase and Lysozyme to investigate the effect of microgravity on the crystallization mechanism. In addition, we obtained much know-how of using GCB.

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In order to verify the impurity depletion zone hypothesis, we developed a new method, which employs a confocal laser scanning microscope for detecting fluorescence of the labeled impurity. This method is capable of visualizing the impurity distribution both inside and surroundings of the crystal. We visualized both the impurity depletion zone around the growing protein crystal, and also the impurity distribution inside the crystal. The impurity distribution inside the crystal revealed that the impurity distribution coefficient in this experiment condition was about .

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Effect of forced solution flow (25 µm /s) equal to natural convection level on morphology and the step growth rate of tetragonal lysozyme crystals was investigated by temperature controlled AFM at 20°C. It was found that macro- step was enhanced when the solution flowed in the same direction of the step motion. The step growth rate reached a maximum and then decreased with experimental time although the protein concentration was kept constant.

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Bubble-free injection of solution into a glass cell is necessary for appropriate crystal growth and in situ observation under the microgravity environment. The injection experiments under microgravity environment were performed with the parabolic flight using MU aircraft. The optimum requirements of inside coating patterns and the injecting speeds were found. In this paper, we discuss the influence of laminar-turbulent flow of injecting condition and the air-water interfacial shape of injecting into the glass cell on successful bubble-free injection.

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The nucleation of silicate materials from the vapor was experimentally investigated under microgravity condition us- ing an aircraft or a dropfacility, for the simulation of the dust formation process in the early solar system. The nucleation of amorphous silicate materials from the vapor in microgravity occurred at the high supersaturation ratio, which ranges from 10 3 to 1083 and the incubation time for the nucleation ranges from 10-8 to 10-10 sec.cm3. The fine particles formed in microgravity are fine crystal particles, the diameter of which is a few hundred nm, while the fine particles formed under normal gravity are amorphous particles, the diameter of which was 0 to 30 nm. We have also applied the laser interferometer for the measurement of the temperature and the gas concentrations. The large increase of the refractive index was found to be due to crystallization near the melt interface in the microgravity experiment. These results indicate the rapid amorphous nucleation followed by crystallization.

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