Two-dimensional crystallization experiments.

Our experience in the growth of two-dimensional crystals of different proteins is presented. Polyethylene glycol was used to produce two-dimensional arrays of haemocyanin from O. vulgaris and of cholera toxin. The arrays showed a hexagonal close-packed structure of only randomly oriented molecules. The increase in protein concentration probably occurred too quickly to allow complete crystallization. Different two-dimensional arrays of hexameric haemocyanin molecules (from P. interruptus) were obtained by microdialysis through the specimen supporting film. A comparison was made with X-ray data. Two-dimensional tetrameric arrays of molecules, possibly rhodopsin, were seen in samples of bovine retinal rod outer segments in the presence of ammonium sulphate. Two-dimensional crystals of complex I (from bovine mitochondria) were prepared by dialysis in the presence of ammonium sulphate. A three-dimensional reconstruction was made from two tilt-series by computer filtration using the direct SIRT procedure. Finally, the possibility of computer crystallization using correlation techniques in combination with correspondence analysis is discussed.