To investigate the effects of gravity for the crystal growth of macromolecules, the effects of acceleration during re-entry and the influence of orbit-radiation in the X-ray range for already grown protein crystals the COSIMA hardware was re-configured. The system now fulfils all needs for a multi-approach crystallization experiment. The achieved crystallization results are equivalent to the best which can be obtained by crystallization techniques used in the laboratories. The modification of the hardware, in particular the newly designed crystallization vials, will be described in detail. In October 1991, COSIMA IV was performed on a Russian re-entry Photon capsule. 99 crystallization experiments were accomodated using three different protein crystallization techniques. Additionally, five already grown crystals were send to analyse the influence of the transport. Four radiation detectors were integrated to measure the radiation dose during the mission. A comparison of space- and ground-grown crystals will be included, which were not influenced by a malfunction of the satellite power supply.

We have grown crystals of two bacterial enzymes, thermolysin fromBacillus thermoproteolyticus and a novel 23 kD lysozyme fromStreptomyces coelicolor, on the unmanned COSIMA-2 space mission. The crystals obtained under microgravity conditions were compared with crystals grown in a ground control experiment using identical hardware, and with those obtained in ‘hanging drops’ in the laboratory. For both enzymes, the space-grown crystals tended to be longer but thinner than their terrestrial counterparts. The diffraction properties of each type of crystals were assessed by collecting nearly complete diffraction data sets using an area detector. Space-grown crystals of the enzymes showed much weaker diffraction than both the ground control and the laboratory-grown crystals. Possible reasons for this are discussed.

For the crystallization of proteins under microgravity conditions, a Chinese re‐entry system was used, in which 101 experiments of 25 different biological macromolecules were accommodated. From the results obtained we conclude that under microgravity conditions crystal growth can only be expected under those crystallization conditions which also permit crystal growthon earth. A number of space‐grown crystals were larger in size and of a better quality in their ability to diffract X‐rays than the corresponding ground control crystals grown at the Chinese launch site. However, the space‐grown crystals have not reached the X‐ray diffraction quality of the crystals obtained under optimal conditions in the home laboratories.