Structure Types of Protein Crystals from Virus-infected Plants

Abstract

FURTHER work on preparations of proteins from virus-infected plants tends to confirm and extend the conclusions expressed in our previous letter¹. We had there shown that both concentrated solutions of these proteins and the material prepared from them by drying gave orientated paracrystals. We have now succeeded in preparing the crystals of Stanley and Wyckoff in an orientated form, after trying unsuccessfully a number of methods, such as flow orientation. The method finally used was that of forcing mother liquor out of the crystals by centrifuging in an unglazed porcelain tube, in a saturated atmosphere. The resulting mush was orientated by rolling between glass slides, at 0° to avoid evaporation, becoming completely transparent in the process. It was mounted in a sealed brass case with bubble thin lindeman glass windows and examined by X-ray and optical methods without loss of water. It proved to be practically indistinguishable—in water content (50 per cent), optics and X-ray pattern at low and high angles—from the preparation previously called wet gel. On being allowed to dry, it likewise turns into a horny mass giving similar X-ray photographs to dry gel, though fainter and with slightly larger spacings, probably due to internal strain. The X-ray pattern obtained from the unorientated crystals shows all the main lines given by Wyckoff and Corey² for their crystals, and we have been able to assign all but four very weak lines on these photographs to definite spots given by the orientated gel. There can therefore remain little doubt that their crystals are substantially identical with ours and with our previously described paracrystals.