"X-ray diffraction of protein crystals"

Date:
1954-1956
Reference:
PP/CRI/H/1/33
Catalogue details

Licence: In copyright

Credit: "X-ray diffraction of protein crystals". Source: Wellcome Collection.

    20/45
    Air-dried Crystals Air-dried crystals are not precisely defined for two reasons First, the dimensions if the unit cell and the degree of disorder usually depend so • ewhat on the method of drying. Slow drying usually produces or© ordered crystal. Second» the cell dimensions and the -water content vary with the hvuniáity though not very greatly certainly much less than they do for wet crystals Reasonable fare sho a therefore he taken to k~ep the huuidi the same for the different sets of easureraents - on the cell dimensions, on > *. -d~ ^ s * density, and on the non-protein content It is convenient to measure the cell dimensions first, and carry out the other,meauements . . Zk tsimk -jUW. U- twv- V J wvk lk>/. at the huwity of the atonshere at the ti me asure The rate of drying can be reduced by obvious methods, such as restricting the entry of the dry air. A less obvious way is to immerse the wet crystals in xylene. The water of the crystal is only slightly miscible with xylene, and because of this it diffuses out of the crystal at very reduced rate. The perfec+ion o~ r an air-dried crystal depends partly on the nature of the crystal. A given protein may have one unit cell which ? spacings of hen dried, still .prives X-ray reflections at 4 À. while a second type of unit cell of the same ! ( the latter awount the more customary for dry crystals ) Thus if several forms of crystal 'exist it is worth while trying them all