Some X-ray measurements on single crystals of tomato bushy-stunt virus

Abstract

X-ray measurements on single crystals of tomato bushy-stunt virus have confirmed that the crystal is cubic body-centred with a cell side of 386 A. for the wet and 314 A. for the dry state. Owing to the large unit cell of the crystal there are many crystallographic planes in a stationary crystal in position to reflect monochromatic X-rays, thus giving rise to a photograph showing concentric rings of discrete reflexions when the X-ray beam is travelling parallel to a crystallographic axis. From such photographs it can be shown that both the Bravais lattice and the cell side can be simultaneously determined for the wet crystal without the need of resorting to oscillation or rotation photographs. It is found that the `ring' effect has completely disappeared in the dry state, and instead the appearance of reflexions near the centre of the photograph suggests that a slight disorientation of internal crystallite regions has possibly taken place. The experiments indicate the necessity for the use of high-intensity sources of X-rays for work on weakly scattering biological materials.