PARTIAL IMPROVEMENT OF CRYSTAL QUALITY FOR MICROGRAVITY-GROWN APOCRUSTACYANIN C-1

The protein apocrustacyanin C-1 has been crystallized by vapour diffus ion in both microgravity (the NASA space shuttle USML-2 mission) and o n the ground. Rocking width measurements were made on the crystals at the ESRF Swiss-Norwegian beamline using a high-resolution psi-circle d iffractometer from the University of Karlsruhe. Crystal perfection was then evaluated, from comparison of the reflection rocking curves from a total of five crystals (three grown in microgravity and two earth c ontrols), and by plotting mosaicity versus reflection signal/noise. Co mparison was then made with previous measurements of almost 'perfect' lysozyme crystals grown aboard IML-2 and Spacehab-1 and reported by Sn ell et al. [Snell, Weisgerber, Helliwell, Weckert, Holzer & Schroer (1 995). Acta Cryst. D51, 1099-1102]. Overall, the best diffraction-quali ty apocrustacyanin C-1 crystal was microgravity grown, but one earth-g rown crystal was as good as one of the other microgravity-grown crysta ls. The remaining two crystals (one from microgravity and one from ear th) were poorer than the other three and of fairly equal quality. Crys tal movement during growth in microgravity, resulting from the use of vapour-diffusion geometry, may be the cause of not realising the 'theo retical' limit of perfect protein crystal quality.