PubMed · 13985837
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H E POWERS. 1962-10-06. Sucrose crystallization.. https://doi.org/10.1038/196058a0
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Stable anhydrous lactulose was produced from lactulose trihydrate by stepwise heating on a fluidized bed. The processes were performed on stable powder forms. The anhydrous lactulose was characterized by an opaque white appearance, a coarse surface structure with random cracks and indentations, a high degree of crystallization, stability under humid conditions, and by X-ray powder diffraction, differential thermal analysis, and differential thermogravimetry. Those characteristics were different from those of the original trihydrate, which was transparent, had a smooth surface and a higher degree of crystallization, was stable under humid conditions and had different X-ray powder diffraction, differential thermal analysis, and thermogravimetric characteristics. The transformation was enhanced when the inlet temperature was 45-55 degrees C or when the temperature of the fluidized bed was over 40 degrees C. At these cutoff temperatures, both crystalline forms were observed.
When the light-harvesting chlorophyll a/b protein complex (LHC-II) from pea thylakoid membranes is co-crystallized with native lipids, an octahedral crystal that exhibits no birefringence is obtained. Cryogenic electron micrographs of a crystal edge showed the crystal to be made up of hollow spherical assemblies with a diameter of 250 A. X-ray diffraction data at 9.5 A resolution revealed the spherical shell of LHC-II to have icosahedral symmetry. A T = 1 icosahedral model of LHC-II, in which the stromal surface of the protein faces outward, was constructed using the previously reported structure of the LHC-II trimer [Kühlbrandt et al. (1994), Nature (London), 367, 614-621]. The present result shows the first example of a well ordered three-dimensional crystal of icosahedral proteoliposomes.
A fragment of the Streptococcus pneumoniae PhtA gene product (residues 18-230) was cloned and overexpressed in Escherichia coli. The purified protein was crystallized using the sitting-drop vapour-diffusion technique. Crystals belong to the monoclinic space group C2, with unit-cell parameters a = 62.19, b = 35.9, c = 72.54 A, beta = 90.01 degrees. The crystals diffract X-rays to beyond 1.2 A resolution.